United Airlines’ flights between London and the US could be disrupted from next month as workers threaten to strike over pay.

Up to 18 flights a day could be cancelled if the industrial action goes ahead, according to the union Unite.

Some 300 operations, customer service and baggage handling staff at Heathrow are voting in a strike ballot, which runs until 11 October.

If they vote in favour of strike action, they could walk out during the October half-term holiday.

Maintenance staff working for American Airlines at Heathrow are also taking part in a separate strike ballot, which ends on 30 September.

Unite said UK-based staff working for United Airlines have been offered a 5% pay rise this year, plus an additional payment, followed by a 4% rise in 2023. The union said the offer amounted to a real-term pay cut as inflation is currently higher than 12%.

The airline has also angered its workforce by threatening to end of long-standing agreement which bars the use of outsourced labour or third-party companies. In a statement, Unite said: “This is a red line for Unite members. If the airline pressed ahead it would undo years of mutual agreement.”