There is clear evidence that party affiliation, not just gender, are the driving forces behind whether a legislator supports tougher policy to ensure fair pay. However, some Republican women in the Senate have broken with their party in support of some pay equity legislation.

Sen. Susan Collins AP Photo/J. Scott Applewhite

A record 98 women will serve in the 113th Congress—20 women in the Senate, and 78 in the House. And in this new Congress, the gender chasm between both major parties is even more stark: Of the 20 women set to serve in the U.S. Senate come 2013, 16 are Democrats; of the 78 women in the House, 58 are Democrats. But Democratic women have indicated a desire to collaborate with their female colleagues across the aisle: Missouri Senator Claire McCaskill recently indicated this, as did New York Senator Kirsten Gillibrand.

Is cooperation possible with respect to the Paycheck Fairness Act, an amendment to the Fair Labor Standards Act of 1938 that was rejected by the Senate this past June? So far, all signs point to a resounding “No.” All Democratic women in the Senate supported the Paycheck Fairness Act, while all five Republican women in the Senate rejected it. There is clear evidence that party affiliation, not just gender, are the driving forces behind whether a legislator supports tougher policy to ensure fair pay. The Senate’s heavily partisan vote count on the Paycheck Fairness Act when it was under consideration earlier this year reveals this. Chances of passing the law are a bit better since Democrats have increased their lead in the Senate by two votes—though the law failed by eight votes.

Why did Republican women in the Senate join their party in opposing the Paycheck Fairness Act? The general consensus among Republicans is that the law is simply too tough on employers and that it would pave the way to excessive litigation. Specifically, the Paycheck Fairness Act would restrict an affirmative defense allowed by 1963’s Equal Pay Act. Known as the “factor other than sex” defense, a defense heavily criticized by women’s rights attorneys, this affirmative defense has enabled employers to withstand liability when they pay male employees more than their female employees based on higher earnings at previous jobs, without evaluating whether the higher earnings are actually rooted in qualifications or higher education. In other words, this defense makes it easier to discriminate. Discrimination is found to be a major cause of the wage gap, along with career and life choices.

The Paycheck Fairness Act would restrict this defense, putting a tougher burden on employers by requiring them to prove that pay disparities are rooted in education, experience or other qualifications. The law gives teeth to the Equal Pay Act which, despite being on the books for 40 years, has not been able to resolve wage discrimination.

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Even though discrimination is still a major cause of the overall wage gap and no other law on the books addresses it effectively, Republican women in the Senate, along with the rest of their party, believe that the Equal Pay Act and the Lilly Ledbetter Fair Pay Act are sufficient. As Maine Republican Senator Susan Collins said after the Senate rejected the Paycheck Fairness Act vote in June:

I support equal pay for equal work. I voted in favor of the Lilly Ledbetter Fair Pay Act ….I remain concerned that [the Paycheck Fairness Act] would unnecessarily expose the small business community to excessive litigation, and impose increased costs and restrictions on businesses that are already struggling to create and maintain jobs in this difficult economic environment.

But Collins remarks may give us reason to be hopeful: she along with four of the five Republican women in the Senate—including Olympia Snowe of Maine, Kay Bailey Hutchison of Texas, and Lisa Murkowski of Alaska—did support the Lilly Ledbetter Fair Pay Act as well as a 2010 bill targeting pay discrimination that was ultimately rejected. (New Hampshire Senator Kelly Ayotte was the lone Republican woman Senator who refused to support either bill.)

By contrast, the only Republican male to support Lilly Ledbetter was then-Senator Arlen Specter.

These four women Republicans’ tendency to break from their party in support of some types of equal pay measures—along with reproductive rights in some instances—aligns with research from the Center for American Women and Politics’ about the impact of increasing the number of women legislators on policy impacting women, regardless of party affiliation. A study focused on the 103rd Congress showed that regardless of whether they carry a “D” or an “R” after their name, women legislators seek to promote policy that will best serve women, and are more likely to cooperate with women across the aisle.

As Gillibrand said last year, “When we have our dinners with the women in the Senate — the Democrats and Republicans—we have so much common ground. We agree on so many basic principles and values. I think if there were more women at the decision-making table, we would get more things done.”

On the specific question of pay equity—one that can affect women so profoundly over the course of their lives—the Senate’s Democratic women should try their best to pull their Republican women colleagues along with them.