Senators are unveiling a new effort to block President Trump's decision to ban transgender individuals from serving in the military.

Sens. Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (D-N.Y.) and Susan Collins Susan Margaret CollinsJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally Momentum growing among Republicans for Supreme Court vote before Election Day MORE (R-Maine) have filed an amendment to the National Defense Authorization Act (NDAA) to block the Pentagon from removing or denying re-enlistment to someone "solely on the basis of the member's gender identity."

The amendment also requires Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE to complete his current review of the Pentagon's transgender policy by the end of the year. They want him to turn over a report to Congress by Feb. 21.

There's no guarantee the Collins-Gillibrand amendment will get a vote. More than 300 potential amendments have been filed to the Senate's version of the NDAA.

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“Any individual who wants to join our military and meets the standards should be allowed to serve, period. Gender identity should have nothing to do with it,” Gillibrand said in a statement.

Collins added that "our armed forces should welcome the service of any qualified individual who is willing and capable of serving our country."

The two have filed a separate proposal that would delay the ban until 60 days after Mattis completes his review.

Mattis is already delaying the new enlistment rules for six months as he reviews the Pentagon's transgender policy.

He has until Feb. 21 to turn over a plan to the White House on how to implement Trump's directive, including how to address transgender individuals who are currently serving in the military.

Senate Armed Services Committee Chairman John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE (R-Ariz.) was among the lawmakers from both parties who criticized Trump for his policy change earlier this year, saying that forcing transgender individuals out of the military was "a step in the wrong direction.”

"The Pentagon’s ongoing study on this issue should be completed before any decisions are made with regard to accession. The Senate Armed Services Committee will continue to conduct oversight on this important issue," he said in a statement.

McCain declined to say on Monday if he would support the Gillibrand-Collins proposal, noting he hasn't seen the language.