Industrial action at British Airways could spread to Scotland as unions consult with more workers over whether to stage strikes over pay.
About 700 mostly check-in staff at Heathrow Airport have already voted to strike over the summer holidays.
But the GMB and Unite unions are also consulting engineers and call-centre staff at Gatwick, Glasgow, Manchester and Newcastle on taking action.
BA said it was "fully committed to work together to find a solution".
Last Wednesday, hundreds of BA workers backed strike action over a 10% pay cut introduced during the pandemic.
The airline has offered staff a one-off payment, equal to 10% of their salary, but GMB members at Heathrow want the full pay cut reversed.
BA said it had made an "offer of a 10% payment which was accepted by the majority of other colleagues".
The BBC understands this includes ground operations, engineering and cabin-crew workers, who are also represented by Unite and GMB.
Wider concerns over pay
The wider consultation ballot is separate to the Heathrow issue and about wider concerns over pay.
A spokesman for the GMB, said: "Thousands of BA engineers at Heathrow, Gatwick and in Scotland along with call-centre staff in Newcastle and Manchester are in the middle of consultative ballot for possible industrial action in a row over pay."
GMB general secretary Gary Smith told the BBC: "I don't think this is going to stop with customer check-in staff. There are many of our members across the BA business who are sick to death of the cuts within the company.
"They've seen the company being run into the ground over many years. And people want to see the pay and conditions restored."
The consultation is being undertaken to gauge turnout as well as what action workers may want to take. It is the stage before a formal ballot would take place over industrial action.
Nearly 1.8million BA customers are set to fly out from Heathrow during July, the month when school holidays begin across the nation.
The earliest Heathrow workers could go on strike would be from around July 7. Unions legally have to give a company 14 days' notice to prepare for action.
Unions have yet to specify dates for the strike, but an announcement is expected soon.
BA said: "We will of course keep our customers updated about what this means for them as the situation evolves."
The company, which is owned by International Airlines Group, has already cut 10% of its flights between March and October.
Airlines and airports have struggled to cope with a resurgence in demand for travel following the Covid lockdown, when the industry cut thousands of jobs as international travel ground to a halt.