Shadow chancellor John McDonnell is joining members of British Airways' cabin crew who are starting a three-day walkout tomorrow.
Unite the union said its general secretary Len McCluskey and the shadow chancellor will be joining the picket lines at Heathrow tomorrow in a dispute over pay.
McDonnell, whose Hayes & Harlington constituency covers Heathrow Airport, said:
I'm joining my constituents in their campaign for fair pay.
There is a genuine sense of grievance amongst these workers, whose wage rate has been cut in half by a company that is making large-scale profits and whose chief executive's salary has increased to a multi-million pound pay out.
This dispute is all about a sense of fairness.
It follows recent comments from Labour leader Jeremy Corbyn saying he'd join a Southern rail picket line and that he felt long-suffering commuters would support his position. Both Corbyn and McDonnell joined the junior doctors' picket line last year.
The 72-hour walkout by members of the Mixed Fleet cabin crew (who fly both short- and long-haul flights) begins at 00:01, and is the next batch of action after last week's two-day strike.
Unite national officer Oliver Richardson said: "Unite urges British Airways to wake up to the deepening anger of mixed fleet cabin crew and start valuing their contribution by meaningfully engaging with Unite to address poverty pay."
British Airways said the last strike had "failed in its objective of disrupting our passengers" and said the pay offer for its "Mixed Fleet" crew members "is consistent with deals agreed with Unite for other British Airways colleagues".
The airline has "further strengthened" its schedule for 19-21 January and "will fly all customers to their destinations". BA has committed to running all of its long-haul services to and from Heathrow, as well as all services to and from Gatwick, London City and Stansted.
"We will merge a small number of our short-haul services at Heathrow, resulting in the cancellation of only one per cent of our total scheduled flights across the three days," a BA spokesperson said. "Customers affected will be able to fly slightly earlier or slightly later."