Senate Democrats, led by five female Senators, began a renewed push this week to pass the Paycheck Fairness Act, a bill that protects women who sue over being paid less than their male counterparts.

But, as with much of the recent pro-woman legislation, the measure will spark a partisan fight. On Thursday, Senate Majority Leader Harry Reid (D-NV) began efforts to prevent the vote from being filibustered. “Republicans deny they’re waging a war on women,” Reid said on the floor Thursday morning, “yet they’ve launched a series of attacks on women’s access to health care and contraception this year. Now they have an opportunity to back up their excuses with action.”

Here are five things you need to know about the Paycheck Fairness Act:

1. The Paycheck Fairness Act is not new: Democrats, however, have struggled to get it passed. Last time it came up for a vote, the House passed it with very little bipartisan support. Then Senate Republicans unanimously voted against the bill. Even if they had passed it, though, then-President George W. Bush vowed to veto it.

2. Pay equity is a real problem: Nearly half of all workers in the United States are women. But women tend to hold lower-paying jobs overall, and even when they have the exact same title as men, they make significantly less. Overall, women make 77 cents to a man’s dollar, and in some professions, specifically high-paying careers, that disparity is much higher. The Paycheck Fairness Act would help close the gap more quickly by providing incentives for employers not to discriminate.

3. Lost earnings have serious consequences: The amount of money an average woman loses to the pay gap could feed a family of four. And while the wage gap is slowly shrinking, at its current rate it won’t actually disappear for 45 years. Still, more women are becoming the primary breadwinners or dual-earners in their family, with nearly 40 percent of women out-earning their husbands and a larger number of women with high degrees entering the job market.

4. Existing law doesn’t go far enough: The Lilly Ledbetter Fair Pay Act ensured that a woman has the proper window of time to sue for pay discrimination. The Paycheck Fairness Act takes significant steps to close loopholes in the original pay discrimination law, the Equal Pay Act, and to ensure that women can investigate whether they are being discriminated against. It also makes stronger penalties so that employers don’t violate pay discrimination laws. Included in the bill, too, is a grant for a salary-negotiation training program for women, who tend to be reluctant to negotiate.

5. Mitt Romney has not taken a position on the bill: After a very awkward moment over the Lilly Ledbetter Act, a spokesperson for his campaign said that Romney “supports pay equity and is not looking to change current law.” But it’s unclear whether this means Romney would support a new piece of legislation that protects women who don’t have full pay equity.

Overall, women get paid 77 cents to a man’s dollar, but we’ve pointed out before that the pay gap is worse for some. And the professions that wind up paying women less can be surprising — the financial and lobbying industries, for example, are among the worst offenders.

Unfortunately, even when women make it to the top of large companies, they still face massive pay gaps. Women CEOs make only 69 percent of what their male counterparts make. This chart from Kevin Drum at Mother Jones points out how that number compares to other professions:

It’s particularly disheartening that a job to which many aspire, and which is known as a rain-making career, is so unbalanced. There’s no need to cry over the amount of money CEOs are earning– it’s still egregiously more than everyone else– but in all cases, no matter the profession, there should still be pay equity.

President Obama officially designated Tuesday as Equal Pay Day, marking the day American women had finally worked the three-and-a-half extra months it takes for them to earn the same as men do in a calendar year. American women make just 77 percent as much as their male counterparts, costing them hundreds of thousands of dollars over their working lives.

In 2009, Obama signed legislation aimed at closing the pay gap that exists between men and women, and Equal Pay Day represented a push for further efforts to address the problem. But the inequities facing female workers apparently don’t exist in the eyes of New Hampshire GOP spokesman Tory Mazzola, who said efforts to close the pay gap were actually about giving a “hand-out to trial lawyers,” WBIN TV reports:

MAZZOLA: Instead of being about fair pay, it’s really about a hand-out to trial lawyers because it expands the areas that people can sue their employers unnecessarily.

Watch a news report:

Still, the GOP hasn’t exactly been sympathetic to the equal pay cause. It fought to prevent passage of the Lilly Ledbetter Act in 2009 and blocked the Paycheck Fairness Act in 2010. The campaign of presumptive GOP presidential nominee Mitt Romney, meanwhile, has struggled to indicate that it is even aware of the problem, and the candidate himself has yet to say exactly where he stands on either piece of legislation.

As of today — which is Equal Pay Day 2012 — women make 77 cents for every dollar that men earn. Over the course of a woman’s career, that disparity adds up to more than $430,000 in lost wages for an individual woman. As Center for American Progress economic analyst Matt Separa noted, the pay gap means that women fall behind economically in a number of ways:

Because of this gap women working full time are able to afford less education, housing, transportation, food, and health care for themselves and their families than their male counterparts. As a result women and female-headed households are more likely to be in poverty and less likely to have health insurance. The pay gap translates into a significant economic disadvantage for women and their families, especially when nearly two-thirds (63.9 percent) of women are now either the primary breadwinner or a co-breadwinner, bringing home at least 25 percent of their family’s income.

With the money lost over her lifetime, a woman could feed a family of four for 37 years, pay for seven four-year degrees at a public university, or simply save the money for retirement, boosting her quality of life when she leaves the workforce:

For some women, of course, the pay gap is even worse. According to a report from the Labor Council for Latin American Advancement, Latina women face a pay gap of 40 percent.

Presumptive Republican presidential nominee Mitt Romney’s campaign struggled to answer a question this morning about whether he supported the Lilly Ledbetter Act, the landmark 2009 law signed by President Obama that gives women greater power to seek restitution for pay discrimination. “We’ll get back to you on that,” Romney’s campaign said on a conference call.

Campaign spokesperson Andrea Saul later clarified that statement, posting on Twitter, “Of course [Mitt Romney] supports pay equity,” and telling Talking Points Memo that Romney “supports pay equity and is not looking to change current law.”

Since Lilly Ledbetter passed, however, little has changed in the way of pay equity for women. Women earn just 77.4 cents for every dollar earned by men, and the gap is even larger for female minorities. Congressional Democrats attempted to rectify that by passing the Paycheck Fairness Act, which would update the 1963 Equal Pay Act by closing many of its loopholes and strengthening incentives to prevent pay discrimination. The law was blocked by Senate Republicans. It was reintroduced again last April and went nowhere.

The Romney campaign did not respond to multiple requests for comment regarding his stance on the issue.

In recent days, Romney has attempted to turn the Democratic message that the GOP is waging a “war on women” back on Obama, blaming the president for the fact that 92 percent of the jobs lost under Obama were held by women. Those claims, as ThinkProgress has noted, are misleading, and Romney’s campaign has thus far been unable to point to specific Obama policies that have directly hurt women.

Women in Massachusetts, the state Romney governed from 2003 to 2007, earn 81.4 cents for every dollar earned by men, above the national average. Romney, however, made his career in the financial sector, which holds the dubious distinction of having the largest gender pay gap of any American industry.

Wisconsin Gov. Scott Walker (R) quietly repealed his state’s equal pay law last week, a decision that will make it harder for victims of wage discrimination to sue for lost earnings and back wages. The law was enacted primarily to address the massive pay gap that exists between male and female workers, which is even bigger in Wisconsin than in other states.

Repealing the law was a no-brainer for state Sen. Glenn Grothman (R), who led the effort because of his belief that pay discrimination is a myth driven by liberal women’s groups. Ignoring multiple studies showing that the pay gap exists, Grothman blamed females for prioritizing childrearing and homemaking instead of money, saying, “Money is more important for men,” The Daily Beast reports:

Whatever gaps exist, he insists, stem from women’s decision to prioritize childrearing over their careers. “Take a hypothetical husband and wife who are both lawyers,” he says. “But the husband is working 50 or 60 hours a week, going all out, making 200 grand a year. The woman takes time off, raises kids, is not go go go. Now they’re 50 years old. The husband is making 200 grand a year, the woman is making 40 grand a year. It wasn’t discrimination. There was a different sense of urgency in each person.” [...]

Grothman doesn’t accept these studies. When I ran the numbers by him, he replied, “The American Association of University Women is a pretty liberal group.” Nor, he argued, does its conclusion take into account other factors, like “goals in life. You could argue that money is more important for men. I think a guy in their first job, maybe because they expect to be a breadwinner someday, may be a little more money-conscious. To attribute everything to a so-called bias in the workplace is just not true.”

Among Grothman’s inaccuracies is the idea that only males “expect to be a breadwinner someday.” In two-thirds of American families, women are either primary or co-breadwinners, and yet they still earn less than their male counterparts in all 50 states.

In 2011, the Wisconsin GOP carried out an extensive war on workers that led to recall efforts for state representatives, senators, and Walker himself. In 2012, Grothman and his colleagues have expanded that war to one on women, meaning a group of workers that was already struggling to keep pace with their male counterparts is only going to fall further behind.