Unite leader Len McCluskey has confirmed British Airways cabin crew will be reballoted over potential strike action after the last vote was declared illegal.
Following a vote in favour of further industrial action last month British Airways informed the Electoral Reform Society (ERS) the ballot has been illegal.
As such any action taken would be unprotected.
No members will be asked to recast their votes as Unite seeks to redress grievances over the withdrawal of travel perks from members following previous strikes.
McCluskey, general secretary of Unite, criticised the airline for not dealing with the union directly.
He said: “BA has launched a legal blitz against the independent scrutineer used to conduct this ballot, the Electoral Reform Society.
“While not addressing the union directly, BA advised the ERS the ballot was unlawful and that any industrial action taken on the basis of it would be unprotected.
“This is merely an assertion by BA – however, the ERS decided, on the basis of protecting its own legal position, to issue a qualification in its official report on the industrial action ballot.”
No dates for the strikes had been announced before Unite was forced into the latest retreat.
Official notice of the new ballot is expected to be delivered to the airline – which recently completed its merger with Iberia – within the next ten days.
The dispute has now been rumbling on for over two years.
Initially focused on the implementation of new contracts for cabin crew at the airline, the dispute has become increasingly bitter, with both sides refusing to back down despite new contracts having been agreed.
In May last year, BA was granted an injunction after the High Court ruled the Unite union had not reported results of an earlier strike ballot correctly to members.
The Unite dispute has already cost BA £150 million and led to 22 days of strikes.