Tanker drivers at an oil refinery have begun a three-day walkout in a row over pensions and pay.
The strike, involving 42 Unite members at Grangemouth, near Falkirk, will run until Monday morning, with striking workers taking turns to man the picket lines.
The drivers, employed by BP, will then observe an overtime ban when they return to work on Monday.
Describing the mood on the picket line, a Unite spokesman said: "They've been on since 4am. They don't want to be here but they're buoyant."
The industrial action comes after 90% of drivers balloted voted for strike action to defend their pension rights and protest at the loss of a company share scheme as a result of the imminent aviation contract transfer from BP to another firm, DHL.
Unite claims some drivers could be up to £1,500 a year worse off over the loss of the share-match scheme and that some stand to lose up to £13,000 a year from their pension on retirement when the changes happen.
The union plans further strike action next week if no resolution to the dispute emerges.
"We've notified the employer that there will be further strikes from next Thursday," the union spokesman said.
"At the same time, we're perfectly happy to get back round the negotiating table with BP, but they're going to need to come up with something that's going to see our members adequately compensated. On Monday morning a ban on overtime begins. For an industry that has its backbone built on overtime, we'll see how that transpires."
A spokesman for BP said its priority was the safe supply of fuel products to its customers. He added: "Since we became aware of the prospect of a strike, we have been working, and continue to work, on contingency plans to minimise any potential disruption to our customers."