A potentially catastrophic strike of railroad workers across the US is starting to spook energy and commodities markets, raising the prices of everything from natural gas to corn loaded onto barges for delivery.

Natural gas futures surged 10% on Wednesday, partially driven by fears that an extended strike will curb deliveries of coal and force power generators to rely more heavily on already tight gas supplies. The premium for corn loaded by barge to be delivered to the Gulf Coast jumped nearly 5% on speculation that more will move by boat should rail cars come to a standstill. 

It could get worse. A US railroad strike, the first in more than 30 years, would deal a major blow to raw-materials markets, further disrupting supplies already ravaged over the past couple of years by crop losses, production cuts and, more recently, the war in Ukraine. Commodities account for half of all freight rail traffic. 

“That’s just an outstanding risk that is slowly coming into market focus,” Eli Rubin, a senior energy analyst at EBW AnalyticsGroup, said in an interview. 

A lack of rail transportation would further stress the grain-barge system, which has already seen an “extremely busy” season due to increased exports amid the war in Ukraine, according to Anton Posner, CEO of the Mercury Group, a logistics service provider.

“There’s just not enough barges out there,” Posner said in an interview. “There’s too little right now to even deal with the current volume, even without a rail strike.”

A shutdown in rail service also threatens to boost gasoline prices, according to American Fuel & Petrochemical Manufacturers, a trade association. Though group said some sensitive regional markets could be left with insufficient fuel, individual refiners haven’t reported similar concerns. 

Nearly all finished gasoline in the US is blended with ethanol, which relies heavily on rail transportation. Ethanol in Chicago was little changed one day after prices leaped 5.6% in the biggest gain since December. The price for so-called RINS credits, which refiners need to buy to comply with the US renewable-fuels mandate when they don’t blend enough biofuel into gasoline, rose to the highest in almost a month, matching a record. 

Meanwhile, a slump in diesel prices may have been partially influenced by major railroads unwinding fuel hedges ahead of an expected drop in their actual consumption, analysts at wholesale-fuel distributor TACenergy wrote in a note to clients.

Duke Energy Corp., which owns utilities in the Carolinas, Florida, Ohio, Kentucky and Indiana, said it has contingency plans in place to limit the impact of coal-supply interruptions if there’s a strike. The company said it has sufficient coal inventories to withstand a limited disruption and can use alternate fuels, such as natural gas and fuel oil, to generate power. 

While the likelihood of a work stoppage is potentially high, the risk of a prolonged strike lasting longer than two days is very low, with Congress expected to act to avoid further impacts, Morgan Stanley analysts including Pamela Kaufman said in a note to clients.

Talks between freight-rail companies and unions continued under Labor Secretary Marty Walsh’s leadership Wednesday as the deadline to avert a strike nears. About 125,000 workers could walk off the job if a deal isn’t reached by Friday’s deadline, with discussions between rail companies and unions not showing signs of progress.

“Secretary Walsh continues to lead discussions at the Department of Labor between the rail companies and unions,” a spokesperson for the department said. “The parties are negotiating in good faith and have committed to staying at the table today.”