Two senators just filed an amendment to block President Donald Trump’s transgender military ban, a move that aims to reverse the controversial order.

The amendment from Sens. Kirsten Gillibrand (D-NY) and Susan Collins (R-ME) would stop the military from kicking out transgender service members solely because of their gender identity, according to a press release sent out by Gillibrand’s office Monday evening. It would also require Defense Secretary Jim Mattis to assess the effects enlisting transgender people would have on the military, and he would have to send the review’s results to Congress by the end of the year.

The senators hope to get a vote on the provision as part of the National Defense Authorization Act — the must-pass $700 billion bill that sets the Pentagon’s budget. The Senate will debate that legislation this week.

But first Senate Armed Services Committee Chair John McCain (R-AZ) must decide if the provision gets a vote, and it’s currently unclear if he’ll allow that to happen. Even if he does allow it, the amendment’s chances of becoming law aren’t good. Forty-five senators including Gillibrand and Collins (the lone Republican) sent a letter to Mattis in July asking him not to kick out transgender troops. For the amendment to pass, it would likely need to get 60 votes.

When Trump tweeted on July 26 that he wanted to bar transgender people from serving in the military, GOP leaders — including McCain and Sen. Orrin Hatch (R-UT) — came out against the decision. But they have yet to indicate they would vote to block the ban in Congress.

Transgender troops were allowed to serve openly since former Secretary of Defense Ash Carter announced they could do so in June 2016, and there are an estimated 1,320 to 6,630 active-duty trans troops according to a 2016 RAND study.