Two months ago, America narrowly avoided a U.S. rail worker strike that could have brought supply chains to a standstill and crippled the economy. Now, that option is back on the table.

In September, four unions representing around 60,000 rail employees reached a tentative agreement with rail companies—with the assistance of the Biden administration—that averted a nationwide strike. But last week, the Brotherhood of Railroad Signalmen (BRS), a rail worker union, voted against ratifying that agreement. Over 60% of the union’s rank and file members voted against it, with the lack of paid sick days being the main sticking point.

“For the first time that I can remember, the BRS members voted not to ratify a National Agreement, and with the highest participation rate in BRS history,” Michael Baldwin, the group’s president, wrote in a statement on Oct. 26.

The BRS is not alone in being unsatisfied with September’s tentative agreement. They join the Brotherhood of Maintenance of Way Employes Division (BMWED)—the third largest rail union in the country—which also voted against the agreement on Oct. 10.

The two unions are still negotiating with railroad companies over a resolution, but time is running out. Without government intervention, rail workers could in theory begin striking if a deal isn’t reached by Nov. 19, a spokesperson for the BMWED told Fortune.

If it does come to a strike, it could have big implications for the U.S. economy. The averted September strike could have cost the country as much as $2 billion a day in supply chain disruptions that would aggravate soaring inflation, according to a study by the Association of American Railroads (AAR), and experts tell Fortune a strike now would have a similar if not greater impact, given the upcoming holiday season.

A strike just ahead of Thanksgiving, and the beginning of the busiest shipping season for retailers, could derail the “main artery” of the U.S. economy, Daraius Irani, chief economist at Towson University’s Regional Economic Studies Institute and railroad economics expert, told Fortune. It could even provide kindling to the smoldering fire of the U.S. recession many economists predict is on the way.

“We’re already facing a supply chain crisis, and now with this on top of it, it could just be a fast accelerant towards a recession,” Irani said. “This would be one of those things that push the economy towards an inflationary recession.”

Congress does have the power to step in and order rail workers not to strike for a certain period of time, but the White House has signaled that unions and companies should be the ones to come to an agreement, and that government intervention may not lead to a permanent resolution to the problem.

The unions and rail companies will return to the bargaining table next week to attempt another deal.