Unite is to raise £700,000 to support striking British Airways cabin crew with an "unprecedented" levy on members, the union has decided.
Officials said the move showed the union's resolve in continuing the bitter row over jobs and cost-cutting, which has cost the airline millions of pounds.
Cabin crew were on strike again on Monday for the third day of a four-day walk-out following a three-day stoppage last week, which BA said has cost it around £50 million.
Unite maintained that BA's losses as a result of the disruption to flights and cost of hiring planes from other companies was nearer £100 million.
A proposal for a mandatory 2% levy for the next quarter to support the BA strikers was approved by the union's general executive, sources said.
Joint leader Tony Woodley said the move was "unprecedented" and would raise £700,000, which will go on strike pay and other ways of supporting union members involved in the dispute.
Meanwhile, British Airways has been accused of paying pilots an "extraordinary" £166-an-hour to cover for striking staff, making them the world's most expensive cabin crew.
Unite said the airline had gone to "enormous lengths" to divert hundreds of pilots from their everyday jobs to work as crew, with the guarantee that they will still be paid salaries of up to £120,000.
The union contrasted the pay with the salary of cabin crew, which it said was £15,000 a year, or £16 per hour, after five years' experience.
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The claim signalled another round in the war of words between the two sides as cabin crew started their third day of a four-day walkout in a bitter row over jobs and cost-cutting.
