The American Civil Liberties Union filed a lawsuit Tuesday on behalf of four American female military members challenging the U.S. Defense Department's policy excluding women from ground combat positions.

The suit, (PDF) filed in U.S. District Court in California, lists four servicewomen as well as the Service Women's Action Network, a nonpartisan advocacy group, as plaintiffs, and says the military's combat exclusion policy is outdated and hinders troop performance in the field.

"Every time a woman, or any combat member, sets foot in Afghanistan or Iraq, they are serving in a combat zone," said one of the plaintiffs, former Marine Captain Zoe Bedell in a Tuesday conference call. "The combat exclusion policy does not reflect this reality. Instead, it creates a complex and dangerous set of rules which prevent commanders from making the best choices in deciding how to fight."

Bedell, who served in Afghanistan, said she left the military because the policy stifled her chances on advancement based on her qualifications.

Major Mary Jennings Hagar, who has served three tours in Afghanistan as a combat search-and-rescue pilot with the Air National Guard, said that while her gender has never been an obstacle in accomplishing her missions, the relatively few people she has encountered with a gender bias against her have the option of using the policy against her.

"I've encountered people who have questioned the authenticity of my story because they are under the misconception that there are no women in combat," Hagar said.

As Reuters reported Tuesday, while some restrictions on womens' roles have been reduced -- some women can now serve in combat batallions, as well as in units required to serve alongside combat troops -- they are still barred from serving in infantry or smaller combat squads.

In a statement, Defense Department spokesperson said on Tuesday that Secretary Leon Panetta "remains strongly committed to examining the expansion of roles for women in the U.S. military, as evidenced by the recent step of opening up thousands of more assignments to women." Panetta is named as a defendant in the lawsuit.

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