Last-ditch talks are taking place between Heathrow Airport and union bosses in a bid to stop planned strike action going ahead.
The UK's busiest airport has already cancelled 177 flights on Monday and Tuesday - roughly one in seven departures - after union members voted overwhelmingly to reject a pay offer.
The Unite Union said 88% of its 4,000 members - which includes security guards, firefighters and engineers - voted down the deal which Heathrow said was worth 7.3% over two and a half years.
Industrial action will currently take place on August 5 and 6, with further strikes planned for August 23 and 24.
Whilst the talks are ongoing, airlines are making arrangements to operate flights from different airports in a bid to avoid further cancellations.
The talks are being held under the chairmanship of the conciliation service Acas.
A spokesperson for Heathrow advised passengers to check their flight status before travelling to the airport and visit Heathrow.com for more information.
They continued: "In preparation for the proposed industrial action on Monday, August 5, and Tuesday, August 6, we have been working closely with our airline partners to identify departing flights which will need to be cancelled from Heathrow.
“While the vast majority of flights will be unaffected, some airlines are making arrangements to operate flights from other UK airports, others will be delaying flights and unfortunately a number will be cancelled.
“Airlines have now started to contact passengers on affected flights and passengers should contact their airline for more information."
Passengers scheduled to fly on Monday or Tuesday and whose flights have not been cancelled, have been told to arrive at least three hours ahead of long-haul departures, and two-hour ahead of short-haul departures, as it may take longer getting through security checks.
Unite has told Heathrow not to pay millions of pounds in compensation to airlines for cancelled flights, but instead use the money to settle the dispute.
Wayne King, Unite regional officer, said: "Heathrow faces a compensation bill in the region of £4.6 million from airlines if the planned strikes go ahead.
"Rather than provoking the disruption that strike action will cause, we would urge Heathrow Airport to use this money for an improved pay offer that better reflects the hard work of the workers who keep the airport running safely and smoothly.
"This latest vote for strike action points to growing anger among the airport's workers in a whole range of vital jobs which are essential to the smooth and safe running of Heathrow.
If you are travelling from Heathrow on the day of the proposed strikes, here are some things to bear in mind, according to the UK Civil Aviation Authority:
If a passenger’s flight is cancelled their airline must rebook them on to an alternative flight, or offer a full refund for the entire booking (ie. return flight as well).
If a passenger experiences a delay at the airport while waiting for their flight, their airline must provide care and assistance (meal vouchers etc) regardless of the cause of the delay.
If a flight cancellation or delay is the result of industrial action taken by third-party employees (ie. airport staff) then an airline is probably not obliged to pay compensation to passengers.
Airports are not legally obliged to pay flight delay compensation to passengers.
Monday and Tuesday's strikes come just days after British Airways lost a bid to stop its pilots from going on strike over pay disputes.