A Democratic congresswoman from Maine is challenging the Marine Corps to change its tattoo policy, arguing that the rules unintentionally discriminate against female recruits.

Rep. Chellie Pingree, a major proponent of progressive causes, sent a letter to Gen. Robert Neller, the Marine commandant, on Friday requesting a review of the tattoo policy. Pingree wants the tattoo rules to be adjusted so that Kate Pimental, a 20-year-old Maine woman who has a tattoo below her collarbone, can be accepted into the service.

Pingree argued that a man with a tattoo in the same place on his body would be allowed to join the Marines because he would be able to cover the marking with the Marine-issued crewneck T-shirt for men. Female Marines are issued V-neck t-shirts, meaning that Pimental’s tattoo would be exposed.

Pimental’s tattoo reads, "Let your smile change the world but never let the world change you."

"I write to you today concerning several policies and regulations that, however unintentional, directly affect female Marines’ opportunities to serve," Pingree wrote in the letter. "As women take more active roles in defending this country, it’s important that we address some of the discrepancies that provide men with options unavailable to their female counterparts."

Last December, Defense Secretary Ash Carter ordered the military to open up all combat roles to women, a decision that Pingree cheered.

Pingree, who has represented Maine’s 1st district since 2009, has repeatedly voted against defense spending legislation. She is the former president and CEO of Common Cause, a progressive nonprofit campaign finance and government reform group headquartered in Washington, D.C., and has long criticized the influence of big money in politics.

Her ex-husband, hedge fund billionaire Donald Sussman, is a major donor to progressive causes and Democratic campaigns. Sussman gave $2.5 million to Priorities USA Action, Hillary Clinton’s Super PAC, last year, according to Federal Election Commission records. Pingree is a maximum donor to Hillary Clinton’s presidential campaign.