The latest is that ground workers at Heathrow have started a three-day strike over a pay dispute.
The Unite union, which represents the workers, says the strike involves 350 workers employed by sub-contractor Menzies.
Unite says it could disrupt flights departing terminals 2, 3 and 4.
Flights operated by Air Canada, American Airlines, Lufthansa, Swiss Air, Air Portugal, Austrian Airlines, Qantas, Egypt Air, Aer Lingus and Finnair are most at risk.
The walk-out is over a "derisory" pay offer by Menzies which is effectively a "real terms pay cut," Travel Mole reported Unite as saying.
“They had every opportunity to make a fair pay offer, but have chosen not to do so,” Unite regional officer Kevin Hall said.
Heathrow Airport said in a statement that it is "in discussions with airline partners on what contingency plans they can implement".
A separate dispute involving Menzies and dnata ground staff was resolved meaning flights taking football fans to the World Cup in Qatar will not be affected.
