The final installment of The Hunger Games movie franchise opened this past weekend. And star Jennifer Lawrence (affectionately known to her fans as J-Law) is saturating the media.

But last month J-Law made headlines for another reason: her essay about gender pay inequity. In her rant, J-Law addressed revelations from the Sony Pictures Entertainment data hack that she and Amy Adams were paid less than their male co-stars in American Hustle. When she found out about the pay difference she wasn’t mad at Sony, she was mad at herself, she wrote.

“I failed as a negotiator because I gave up early. I didn’t want to keep fighting over [the money].” A need “to be liked” and fear of appearing “difficult” kept her from demanding more money, she said. And, “based on the statistics, I don’t think I’m the only woman with this issue.”

Does J-Law know what she’s talking about? The data and the law seem to back her up.

Research studies suggest that on average women are less likely than men to negotiate for more pay; and, when they do, they are less likely to be successful and more likely to face backlash. Employers need to be aware of this dynamic, because it can unwittingly lead to pay disparities that expose them to low morale, talent flight, and legal challenges. 

The Equal Pay Act prohibits sex-based wage disparity for equal work at the same establishment. The jobs do not have to be identical, but they must be substantially equal in terms of skill, effort, and responsibility, and working conditions. But pay differences are permitted if based on seniority, merit, quality or quantity of production, or another factor other than sex. 

However, courts and the EEOC have made it clear that “market forces” or the ability to negotiate a better salary are not defenses to equal pay claims. Last year a court rejected an employer’s argument that it was justified in paying a female employee less than a male employee for doing the same job because the male employee had negotiated for a higher salary, but the female employee had not.

In a well-known case from a few years ago, a Missouri company promoted its female HR manager, who had been making $41,500, and backfilled her position with a man, who was paid a starting salary of $62,500. After discovering the pay disparity, the old HR manager sued. The company argued that its pay decision was justified because the replacement was the best candidate for the job, and he required a starting salary of $62,500, based on what he was earning at his old job, which was the going market rate. The court ruled that while this might justify the new HR manager’s salary, it did not justify the lower rate paid to the old HR manager. The company also argued that the old HR manager’s salary resulted from a prior hiring policy that set lower salary rates, whereas the new HR manager was hired under a new salary structure. That defense did not fly either. 

Cases like these are good reminders that salary history, the market, and salary demands, standing alone, are not defenses to gender-based pay disparities. If employees hold the same job or perform substantially equal work, the employer must be able to identify skills, experience, work quality or quantity, or some other legitimate factor to explain any pay gaps between men and women. 

So how did things turn out for J-Law? After the Sony leak, she made news for negotiating a significantly higher salary than Chris Pratt, her co-star in the upcoming film Passengers. Perhaps taking a cue from her Hunger Games persona Katniss Everdeen, J-Law proclaimed, “I’m over trying to find the ‘adorable’ way to state my opinion and still be likable.”