U.S. District Judge David Lawson said plaintiffs who have lost benefits or been forced to buy expensive private health insurance have made a "plausible claim" that the law violates the Equal Protection Clause of the U.S. Constitution.
Friday's decision came nearly a year after Lawson heard arguments in the lawsuit, filed by the American Civil Liberties Union.
"It is hard to argue with a straight face that the primary purpose ... of the statute is other than to deny health benefits to the same-sex partners of public employees," Lawson said as he ordered an injunction. "But that can never be a legitimate governmental purpose."
The law was approved in 2011 by the Republican-controlled Legislature and signed by Gov. Rick Snyder. It ended insurance for people whose domestic partners work for certain public employers. It's somewhat narrow, exempting colleges and universities, as well as most state government workers whose benefits are set by the Michigan Civil Service Commission.