Sen. Jon Tester, D-Mont., on Wednesday called for the resignation of William Mercer as U.S. attorney for Montana.

In a press release, Tester referred to The Washington Post story that detailed how the federal law was changed to allow Mercer to serve both as Montana's U.S. attorney and as a high-ranking official at the Department of Justice.

"He should resign his post as Montana's U.S. attorney immediately," Tester said in a statement.

"For months, I gave Bill Mercer the benefit of the doubt that he was shooting straight with me and with the people of Montana," Tester said. "Mr. Mercer has been given every opportunity to do right by the people he represents; he has passed on that chance too many times. Mr. Mercer was operating outside federal law, so he had the law changed. That might work in Alberto Gonzales' Justice Department, but it's not how we do business in Montana."

The state's senior senator, Democrat Max Baucus, said Mercer "is not serving the public by trying to wear two hats."

"He needs to choose which job he wants and give it 100 percent," Baucus said.