Sen. Pat Toomey and a group of Republicans are calling on GOP congressional leadership to hold a vote on the U.S.-Mexico-Canada Agreement on trade during Congress' upcoming lame duck session to prevent Democrats from watering down the deal when they take the majority in the House next year.

"President Trump should work with congressional Republicans to incorporate additional free-trade features in the USMCA’s implementing legislation so that it can be passed before the next Congress is sworn in on Jan. 3, 2019," Toomey wrote in an op-ed Wednesday for the Wall Street Journal. The op-ed follows on a letter sent Tuesday by Toomey and 11 other GOP senators making the same plea.

Senate Majority Leader Mitch McConnell, R-Ky., has previously said that the deal will not come up for a vote before the current Congress adjourns, claiming they have simply run out of time to properly finish this year.

Toomey conceded that it would be difficult to have a vote in the upcoming post-election lame duck session of Congress, but argued it was worth trying to prevent Democrats from getting leverage to alter the deal's terms.

"Considering the USMCA before the end of this year would require a process more expedited than some of my colleagues would prefer. However, it may be the president’s best shot at securing a vote on USMCA, and preserving the North American trading relationship," the Pennsylvania senator said.

Ordinarily, Congress is limited in how it can alter trade deals. Trade Promotion Authority, the law passed by Congress setting negotiating terms for the administration, limits them to simple up or down votes on passage of deals. However, the language how on the deal's provisions will be implemented is unfinished, and many lawmakers and outside groups see that as a means to alter the USMCA deal. Toomey argued that the GOP can do the same thing.

"If President Trump chooses to pursue a USMCA vote in Congress this year, I will engage in a good-faith effort to work with his administration on implementing legislation that corrects the flaws [in the deal] and that could pass Congress with the votes of free traders like me," he said.