Some Republicans in US Congress try to close government over vaccine mandates
Senate Minority Leader Mitch McConnell. (Mande Ngan/AFP)

By Susan Cornwell and David Morgan

WASHINGTON (Reuters) - U.S. lawmakers' efforts to keep the U.S. government operating hit a stumbling block on Wednesday as a group of hard-line Republicans threatened to try to block any plan that allowed COVID-19 vaccine mandates to proceed.

Congress has until midnight on Friday to pass a measure continuing to fund federal government operations or face a partial shutdown during a pandemic that would be a political embarrassment to President Joe Biden's Democrats, who narrowly control both chambers of Congress.

The hard-line Republican House Freedom Caucus called on Senate colleagues on Wednesday to vote against any measure, known as a "continuing resolution," that would support Biden's requirements that workers at federal contractors and large companies receive the COVID-19 vaccine.

"Use all procedural tools at your disposal to deny timely passage of the CR unless it prohibits funding - in all respects - for the vaccine mandates and enforcement thereof," the group wrote in an open letter to top Senate Republican Mitch McConnell.

McConnell earlier in the week said he was confident that the measure funding the government would pass. House Republicans do not have enough votes to block legislation. But most legislation requires 60 votes to advance in the evenly divided 100-seat Senate, so Democrats would need support from at least 10 Senate Republicans to get to a vote on passage.

Democratic Senate Majority Leader Chuck Schumer told reporters talks with McConnell on funding the government were "making good progress". He dismissed the Freedom Caucus' threat.

"We'll have total chaos," Schumer said. "It's up to the leaders on both sides to make sure that doesn't happen." Other lawmakers suggested one way to solve the problem would be to allow a separate vote on the vaccine mandates.

Negotiations between the two parties are focused on how long to continue to fund the government. Democrats want to extend current funding levels just until January and then pass new spending bills, while Republicans have urged a delay until later in the spring, a move that would leave spending at levels agreed to when Republican Donald Trump was president.

The Biden administration was blocked in court on Tuesday from enforcing two mandates requiring millions of American workers to get vaccinated against COVID-19, a key part of its strategy for controlling the spread of the coronavirus.

One federal judge temporarily blocked enforcement of a government mandate for healthcare workers. Another blocked the administration from enforcing a regulation that new government contracts must include clauses requiring that contractors' employees get vaccinated.Democrats were indignant at the conservative Republicans' demand. "I think we're in the middle of a public-health crisis. And vaccine requirements are reasonable public-health measures at this particular point in time," House Democratic Caucus Chairman Hakeem Jeffries told reporters.

(Reporting by Susan Cornwell and David Morgan, additional reporting by Moira Warburton; Editing by Scott Malone and Mark Heinrich)