Heathrow Airport in London, UK. (Photo: VCG) 

Heathrow Airport has cancelled 172 flights Monday and Tuesday amid strike plans by thousands of workers.

Members of the Unite union overwhelmingly rejected the airport's 7.3 percent pay increase offer.

The airport says it has asked airlines to consolidate flights and rebook passengers on alternative services in advance. Passengers are also being advised to contact their airlines to seek the most up-to-date information.

Security is also expected to take longer than usual and passengers are being advised to prepare.

Union leaders are set to meet with Heathrow's management Saturday after talks dragged late into the night on Friday.

As a major international airport in UK, Heathrow is one of the busiest airports in the world by international passenger traffic.