Updated October 26, 2022 at 5:18 PM ET

A second railroad union voted on Wednesday against ratifying the tentative agreement brokered between the railroad managers, unions and members of President Joe Biden's administration. The move increases the possibility of a strike in November that would endanger the national supply chain if a deal is not reached.

The Brotherhood of Railroad Signalmen, which represents over 6,000 workers in the United States, announced that its members voted to reject the tentative agreement, sending the union back to the bargaining table with management.

In a statement, union president Michael Baldwin notes that it's the first time the union has voted against ratifying an agreement.

Sick leave policies continue to be at the center of talks. Unions argue current policies don't allow workers to take personal or sick time off. While the presidential emergency board (PEB) appointed by President Biden negotiated increases in wages, it did not address the leave policies.

"I have expressed my disappointment throughout the process in the lack of good-faith bargaining, " Baldwin said in the statement.

"Additionally, the highest offices at each Carrier, as well as their stockholders, seem to forget that the rank-and-file of their employees continued to perform their job each day through an unprecedented pandemic, while the executives worked from home to keep their families safe," Baldwin said.

BRS, which represents workers who install and maintain signal systems, is not the only one. The Brotherhood of Maintenance of Way Employees, the third largest railroad union, voted earlier this month to also reject the agreement. All 12 unions would need to independently accept a deal in order to avoid a potential strike.

"We're going to go back to the table and we are going to talk to them, talk to the railroads about increased paid sick days because our members have made it very clear to us that the lack of paid sick days is a very significant issue for them," Peter Kennedy, BMWED's chief negotiator previously told NPR.

Biden's influence is on the line

On Wednesday, White House Press Secretary Karine Jean-Pierre reiterated that the priority is to avoid a shut down and that the administration is in regular contact with both sides.

"It is the responsibility of the parties involved to resolve this issue and any idea that kicking this to Congress will result in a quick or favorable outcome is deeply misguided," Jean-Pierre said. "These unions' rejection of the current proposed contract does not mean we face an immediate rail shut down, that's not how we view it. But it does mean the unions and their employers have additional work to do."

Jean-Pierre said the administration urges good faith negotiations to avoid a shutdown of rail operations.

In September, members of Biden's cabinet pushed to get railroad management and unions to come to an agreement after nearly two years of ongoing contract negotiations.

Railroad unions were threatening to strike, leading some services like Amtrak to preemptively be affected.

Labor Secretary Marty Walsh stayed up overnight brokering the tentative agreement ultimately accepted by the representatives. But although the agreement was viewed as a major labor win by the President, the union members still have to vote.

Biden has long proclaimed himself as the most pro-labor president, often having union members introducing him ahead of speeches.

But even after the agreement was reached, many railroad workers were still picketing in disapproval of the deal.

A threat of a strike grows

The union's rejection means that now they're in what's called a "status quo" period that will run until Nov. 19 — five days after Congress is scheduled to come back to Washington. A strike would not come before then. Congress could prohibit a strike and force unions to accept the deal.

So far, six unions have voted in favor and two have voted against, but all could strike if one does, putting at risk the transportation of up to 40 percent of goods, right ahead of the holiday season.

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