It is the first time that official picket lines have been seen on the Crossrail project

Around 80 electricians have downed tools over the contractor’s refusal to pay them a finishing bonus on the job.

Workers are demanding finishing bonuses of up to £5,000 a head.

Unite regional officer Guy Langston, said: “This is the first time that strike action will take place on Crossrail this will cause disruption and inevitably delay the project.

“The strike was announced before Christmas, giving Balfour Beatty every opportunity to resolve the dispute through negotiations but they have declined to do so.

“Industrial relations on the entire Crossrail project have been steadily deteriorating and Unite will continue to fully support our members when further industrial issues develop during the lifetime of the project.”

The union said a finishing bonus is standard practice on comparable major projects.

Unite said: “It allows workers to give notice on their lodging, without suffering financial loss.

“All the electricians employed at Woolwich live outside London and have had to arrange temporary accommodation while employed on Crossrail.”

The union added: “If the dispute is not resolved further strike dates are expected to be announced in the coming weeks.”

Balfour Beatty said: “We are aware of the 24 hour strike planned for 10 January.

“Balfour Beatty engaged fully with Unite to negotiate and agree a productivity bonus for Balfour Beatty Kilpatrick’s workforce of electricians on Crossrail.

“Since then, Unite demanded a significant increase in the bonus level and a completion bonus.

“We will continue to engage with our workforce.”