Transport workers delivering fuel to Tesco forecourts are to stage a two-day strike in a row over jobs.
The Transport and General Workers Union said drivers based at Purfleet in Essex, Avonmouth and Cardiff will walk out next Wednesday and Thursday.
The 140 drivers fear their jobs, pay and conditions are under threat because of plans to transfer their employment from Wincanton to another firm, TDG.
On Thursday, TGWU spokesman Ron Webb confirmed the action would take place.
A spokeswoman for Tesco said: "The two companies involved are still in discussions.
"We are hopeful that a strike will be avoided and are confident that Tesco fuel supplies will not be affected."