When Marie Villegas, 46, an IT project manager, was about to start a new position with the Department of Defense contractor she works for, she Googled "salary negotiation tips."

"I knew my responsibilities would increase, but I wasn't sure how to actually ask for more money," she said.

That's how Villegas learned about a free salary negotiation session coming up that weekend in Washington, D.C., where she lives. It was geared toward equipping women with tools and tactics to lobby for more pay and better benefits.

Villegas left the workshop with a plan. That same day, she emailed her manager to request a meeting. When they met, she laid out her points and he was receptive, she said, and agreed to meet her in the middle.

While Villegas didn't get the $20,000 raise she asked for, she was offered a $10,000 pay hike for her new role.

"I still consider it a big win since I could have ended up without any raise at all if I hadn't pursued it," she said.

Many women are aware that a woman in the U.S. generally makes about 80 cents to each dollar a man earns.

Much of that shortfall has been explained by criteria such as education and work experience — women are more likely to work part time and take time off over the course of their careers, often to care for children or other family members, according to the Pew Research Center.

But there are other factors that are more difficult to measure, such as gender discrimination, which may contribute to the ongoing wage discrepancy, Pew said.

Additional research suggests that more discrepancies arise when it comes to negotiating pay. In fact, women ask for raises as often as men, but they are less likely to receive the raises they requested.

Women are also twice as likely as men to say they are not at all comfortable asking their boss or supervisor for a raise, according to a report by Zoro, an online retailer of industrial supplies and business products.

Before even approaching the conversation, women were significantly more likely than men to research salary ranges and rehearse the conversation, but still more likely to postpone asking until an annual or semiannual performance review, Zoro found.