United Parcel Service workers represented by the Teamsters voted Friday by a 97% margin to authorize a strike, which would be the biggest for a single employer in U.S. history.

The union vote now sets a seven-week countdown until worker contracts expire on July 31. If an agreement between the union and the company isn’t reached by then, the workers could begin striking the following day, a move that would have enormous economic consequences.

“This vote shows that hundreds of thousands of Teamsters are united and determined to get the best contract in our history at UPS,” said Teamsters General President Sean O’Brien. "If this multibillion-dollar corporation fails to deliver on the contract that our hardworking members deserve, UPS will be striking itself.”

This story is breaking and will be updated.