Women make up about 14 percent of active military personnel. Recently, 14,500 positions were opened up for women to apply, but one major restriction still exists: by law, women are not allowed to join ground combat units. That also means women cannot earn the prestige and pay that comes with certain high-profile assignments.
The four women say they engaged in combat during their tours in Iraq and Afghanistan. Three of the women are in the reserves. A fourth leaves active duty this week.
The lawsuit also alleges that women are already serving unofficially in combat units.
"Every time a woman or any service member sets foot in Iraq or Afghanistan, they are serving in a combat zone," said Marine Corps Capt. Zoe Bedell, one of the plaintiffs in the latest lawsuit.
More than 144 female troops have been killed and more than 860 have been wounded in Iraq and Afghanistan since the wars began, according to Pentagon statistics.
"I received shrapnel wounds through my face and arms and a burn on my back," said Army Reserves Staff. Sgt. Jennifer Hunt, another plaintiff.
The four women joined the American Civil Liberties Union in suing the Department of Defense, saying they want women to have the chance to compete.
"The policy has the affect of closing whole career fields to service women and closing hundreds of thousands of positions to them," said ACLU attorney Ariela Migdal.
Some opponents question whether women are physically up to the job. The first two women who tried the grueling 13-week Marine infantry training failed the physical test.
The Associated Press contributed to this report.