Senate Democrats are urging top negotiators on a mammoth defense bill to keep a plan requiring that Confederate-named bases be renamed in the final agreement. 

Thirty-seven Democrats sent a letter, led by Sen. Elizabeth Warren (Mass.), to top members of the House and Senate Armed Services Committees as both chambers are expected to formally vote to start negotiations as soon as next week. 

"We strongly oppose removing this provision and respectfully request the conferees to retain in the conference report the provision endorsed by both chambers: a requirement for the Department to rename all military assets named for the Confederacy no later than three years after the date of enactment," the senators wrote. 

Language requiring that Confederate-named bases and other military installations be changed is one of the largest sticking points for getting an agreement on a final National Defense Authorization Act (NDAA), a mammoth bill that broadly outlines defense policy. 

Both chambers passed their initial versions of the bill earlier this year that requires the change, sparking a veto threat from President Trump. 

The House bill requires the names to be changed in one year. The Senate bill gives three years before the names have to be changed. 

The Democratic senators added in their letter that it was "long past the time to correct this longstanding, historic injustice. " 

"Millions of servicemembers of color have lived on, trained at, and deployed from installations named to honor traitors that killed Americans in defense of chattel slavery. Renaming these bases does not disrespect our military – it honors the sacrifices and contributions of our servicemembers in a way that better reflects our nation’s diversity and values. We know who these bases were named for and why they were named," they wrote.

The push from Democrats to keep language in the final agreement comes as Senate Armed Services Committee James Inhofe (R-Okla.) has signaled that he expects the language to ultimately be removed. 

The House and Senate still need to formally form a conference committee to work out a final agreement on the NDAA. But how Inhofe would get the language taken out of a final deal is unclear since Democrats would likely object. 

Trump tweeted earlier this year that Inhofe had committed to ensuring a requirement to rename Confederate-named military bases is stripped from the annual defense policy bill.

“I spoke to highly respected (Chairman) Senator @JimInhofe, who has informed me that he WILL NOT be changing the names of our great Military Bases and Forts, places from which we won two World Wars (and more!),” Trump tweeted.

Inhofe's office said at the time that the tweet spoke for itself. Inhofe separately told the Oklahoman that, “We’re going to see to it that provision doesn’t survive the bill." 

But NBC News reported shortly before Defense Secretary Mark Esper was ousted that he was working with lawmakers to create legislation that would remove the names of Confederate leaders from military bases. 

Three officials told NBC News that Esper intended to work with Congress to put language in the NDAA to cement into law name changes at military installations. 

He also reportedly provided a written framework to Pentagon leaders for stripping out the Confederate names, which could possibly extend to ships and street names on bases, the officials said.