Republican Sen. Marco Rubio pushed back on Biden's move to have Congress ratify a rail contract.
Rail workers threatened to strike - potentially devastating the economy - over a lack of paid leave.
Biden called on Congress to step in and avert a strike by passing the tentative agreement.
President Joe Biden this week stepped in to avert a railroad workers' strike and keep rail infrastructure running, even as workers call for a better contract with access to paid sick leave. Now he's attracted the ire of Republican Sen. Marco Rubio of Florida.
"The railways & workers should go back & negotiate a deal that the workers,not just the union bosses,will accept," Rubio tweeted on Tuesday. "But if Congress is forced to do it,I will not vote to impose a deal that doesn't have the support of the rail workers."
In a statement on Monday, Biden said he was calling on Congress to "pass legislation immediately to adopt the Tentative Agreement between railroad workers and operators - without any modifications or delay - to avert a potentially crippling national rail shutdown."
Congress is able to vote to step in and impose a deal for rail workers, overruling the normal bargaining process. That would shut workers out from striking and from further negotiating over access to paid leave, a key issue for union members. Some Senate Republicans in September called on Congress to step in and force through a deal.
Reuters reported that workers wanted 15 paid sick days, while railroad companies agreed to just one paid personal day in the tentative agreement.
"As a proud pro-labor President, I am reluctant to override the ratification procedures and the views of those who voted against the agreement," Biden said. "But in this case - where the economic impact of a shutdown would hurt millions of other working people and families - I believe Congress must use its powers to adopt this deal."
Secretary of Transportation Pete Buttigieg echoed Biden's sentiment. The pro-business US Chamber of Commerce has estimated that a strike could cost the economy $2 billion a day and bring a slew of services to a standstill.
While Rubio struck out at union bosses, the contract process requires union members to vote on whether to ratify the tentative agreement. The industry's biggest union, alongside three others, voted it down, while the rest of the 12 total unions involved in the negotiations voted to ratify.
The lack of sick leave in the deal has elicited pushback from workers and politicians alike. Ro Khanna, a Democratic representative from California, tweeted on Tuesday: "Am I missing something here? Why wouldn't the rail companies just allow workers to have paid sick days? The new agreement only gives them 1. That's absurd. We need to stand with workers. This is not complicated."
Michael Paul Lindsey, a locomotive engineer in Idaho and steering committee member for Railroad Workers United, told Insider it was a "blatant betrayal" but he wasn't surprised.
"I thought it was kind of laughable that anyone would think that either the Democrats or the Republicans actually cared. Bottom line, they care about money," he said.
Even so, he added, "there was always that hope in the back of my mind that maybe someone would do something that was actually right for the American worker for once - instead of just what's right for corporate America."