Senate Majority Leader Chuck Schumer speaks at the US Capitol in September 2021 in Washington.
CNN  — 

Lawmakers will try and pass a short-term government funding extension by a Friday deadline, but a handful of Republican senators is threatening to gum up the works, raising questions about when the Senate will actually be able to vote.

Senate Majority Leader Chuck Schumer warned on Tuesday that “before the end of the week, the Senate must come to an agreement to pass a short-term extension of government funding,” ahead of the February 18 deadline.

He reiterated that he remains “optimistic” that Democrats and Republicans will keep working together to reach a deal and pass a broader, full-year government spending package. But “in the meantime, both sides should come to an agreement to make sure … the continuing resolution, the short-term funding of the government, is passed by this chamber and avoid any even hint of a government shutdown,” he said.

The House of Representatives voted last week on a bipartisan basis to pass a short-term funding bill, known as a continuing resolution, to extend funding through March 11. Now, the Senate must also pass the measure before it can be sent to President Joe Biden’s desk to be signed into law.

The expectation on Capitol Hill is that neither party wants a shutdown and the extension will pass the Senate before the deadline. But some Republicans are making demands tied to the vote.

A group of six conservative senators is warning they will oppose expedited passage of the stopgap bill to fund the government unless they get a vote to defund the remaining vaccine mandates the Biden administration imposed.

GOP Sens. Mike Lee of Utah, Roger Marshall of Kansas, Cynthia Lummis of Wyoming, Mike Braun of Indiana, Rand Paul of Kentucky and Ted Cruz of Texas signed onto a letter suggesting they won’t agree to a quick vote on the stopgap bill without an agreement for a vote on an amendment defunding enforcement of vaccine mandates.

“We will continue to stand against these mandates until they are discontinued in ambition, design, and practice,” they wrote. “For that reason, we are writing to let you know that we will not consent to a time agreement that eases passage of the Continuing Resolution … now before the Senate absent an agreement to allow for a roll call vote on an amendment that defunds the enforcement of these vaccine mandates for the spending period covered by the CR.”

A similar scenario played out back in December, but the standoff ended with an agreement to hold votes on a stopgap bill as well as a GOP amendment to prohibit the use of federal funding for Covid-19 vaccine mandates, which ultimately failed.

The vote, however, failed with two Republican absences. With Democrats down a member – Sen. Ben Ray Lujan of New Mexico is absent after a stroke – another vote could be tight. Democrats have not announced if they would give Republicans a vote at all.

At a news conference on Tuesday, Senate Minority Leader Mitch McConnell dismissed concerns about the likelihood of a government shutdown if the House-approved stopgap bill is not passed by the Senate this week.

“As is often the case, we’ll process a few amendments before doing the short term CR,” the Kentucky Republican said. “I think it’ll all be worked out. There’s no danger of a government shutdown.”

This story has been updated with additional developments Tuesday.

CNN’s Morgan Rimmer and Manu Raju contributed to this report.