Members of one union rejected a tentative deal with the largest U.S. freight railroads Wednesday, while two ratified agreements and three others remained at the bargaining table just days ahead of a strike deadline, threatening to intensify snarls in the nation’s supply chain that have contributed to rising prices. 

About 4,900 members of the International Association of Machinists and Aerospace Workers District 19 voted to reject the tentative agreement negotiated by IAM leadership with the railroads, the union said Wednesday. But the IAM agreed to delay any strike by its members until Sept. 29 to allow more time for negotiations and to allow other unions to vote.

Railroads are trying to reach an agreement with all their other unions to avert a strike before Friday’s deadline. The unions aren’t allowed to strike before Friday under the federal law that governs railroad contract talks, which include BNSF, Union Pacific, Norfolk Southern, CSX, Kansas City Southern and the U.S. operations of Canadian National.

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