By Katie Johnston Chase and Chris Reidy
Boston.Com

A Boston Cigna HealthCare employee is seeking $100 million in damages in a lawsuit that alleges the company systematically discriminates against women.

The suit states that Cigna treated Bretta Karp and other female employees less favorably than their male peers by denying women rightful promotions and pay raises and fostering a hostile work environment. The lawsuit, which is seeking class-action status, was filed in the US District Court yesterday by the Washington, D.C., law firm Sanford Wittels & Heisler LLP.

Cigna HealthCare, part of Cigna Corp., a global health services company with headquarters in Philadelphia and Bloomfield, Conn., and 30,000 employees worldwide, responded to the lawsuit in a prepared statement yesterday.

“We are committed to diversity and equal opportunity,’’ the company said. “Our workplace policies expressly prohibit discrimination in any form and we intend to fully defend against the complaint.’’

Karp, of Shrewsbury, joined Cigna in 1997 and now manages Cigna’s Massachusetts and Rhode Island provider networks, consisting of hospitals, physician groups, and other health care providers.

Despite receiving favorable reviews and winning performance awards, Karp had her pay and title reduced without explanation, according to the lawsuit, and two of her markets, New Hampshire and Vermont, were reassigned to men. Last summer, Karp was told she was not given a promotion, which went to a less experienced male employee, because she “came across as too aggressive’’ in the interviews, the suit states.

Karp’s lawyer, David Sanford, said the suit could potentially involve thousands of women. Besides $100 million in monetary damages, it seeks structural changes in promotion, performance evaluation, and other practices at Cigna to prevent further gender discrimination.

“The idea that women continue to make 78 cents on the dollar for doing comparable work is something that is a big problem in this country,’’ Sanford said. “It’s not only Cigna’s problem, it’s a societal, systemic problem.’’

Sanford’s firm has had success with similar lawsuits. The firm represented the 6,000 female employees of Novartis <http://finance.boston.com/boston?Page=QUOTE&Ticker=NVS>  Pharmaceuticals Corp. who last spring were awarded $253 million in punitive damages, the largest employment discrimination verdict ever awarded.

But I. Glenn Cohen, assistant professor at Harvard Law School, said Karp doesn’t have an easy road ahead of her.

“Employment discrimination cases are difficult to win in the best of times,’’ he said. “Bringing it as a class action adds a whole bunch of additional hurdles.’’

Still, discrimination suits are sometimes the only way to advance workers’ rights, said Paula Brantner, executive director of Workplace Fairness, a Washington, D.C., nonprofit that promotes employee rights.

“If no one had the courage to file a lawsuit, then employers would learn that they could trample on people’s rights,’’ she said.

Katie Johnston Chase can be reached at johnstonchase@globe.com. Material from Bloomberg News was also used.