The Senate on Thursday defeated a Republican amendment seeking to block President Biden's vaccine-or-test mandate for businesses with 100 or more workers.

Republicans and Democrats were split down the middle on the vote, 50-50 in the upper chamber, falling short of the 60 votes needed to pass the measure.  

Sen. Roger Marshall (R-Kan.) offered the measure, which would block the use of federal funds for vaccine mandates. It came during a series of votes on amendments to a stop-gap government funding measure. 

Biden announced earlier this month that his Department of Labor would put forward a regulation requiring that businesses with 100 or more employees mandate employees are vaccinated, or get tested once per week. 

Marshall said that while the "vaccine has saved lives," taking it should be a "personal choice."

"Simply put, we must not allow the Administration’s unconstitutional vaccine mandate on private companies to go forward," he added. 

Sen. Patrick Leahy (D-Vt.) spoke out against the amendment, pointing to the almost 700,000 Americans who have died of COVID-19, noting the flags marking their deaths. 

"Drive down the Mall and look at the flags by the Washington Monument," he said, noting the amendment "weakens one of our strongest tools to get people safely through this crisis." 

Republicans have largely denounced Biden's move, saying it was an infringement on their personal freedom.  

"Forcing main street to vax or pay a fine will not only crush an economy he's put on life support—it's flat-out un-American," House GOP Leader Kevin McCarthy (Calif.) tweeted earlier this month in response to Biden's announcement. "To Joe Biden, force is more important than freedom. Americans won't stand for it." 

Senate Minority Leader Mitch McConnell (R-Ky.) has frequently encouraged people to get vaccinated, and has been less outspoken against Biden's mandate than McCarthy, but he also voted for the amendment on Thursday.  

The move has been largely praised by health experts, though, as a way to break through to holdouts who still have not gotten vaccinated and have not responded to voluntary measures like incentives. About 23 percent of U.S. adults have not gotten any shots. 

Ashish Jha, dean of the Brown University School of Public Health, called Biden's vaccine mandate "essential to creating a safe work environment." 

"We’re going to protect vaccinated workers from unvaccinated co-workers," Biden said when he made the announcement. "We’re going to reduce the spread of COVID-19 by increasing the share of the workforce that is vaccinated in businesses all across America."

Democrats have increasingly embraced vaccine mandates as a popular issue that is key to getting the pandemic under control. 

An Axios-Ipsos poll this month found that 60 percent of the public supported the vaccine-or-test mandate for businesses.