LONDON (AP) — Heathrow Airport officials and union leaders are holding last-ditch talks in hopes of averting a strike at Europe's busiest airport.

Security guards, firefighters, engineers and drivers at Heathrow plan to go on strike at one minute after midnight if Sunday's negotiations fail. The airport cancelled more than 170 flights scheduled for Monday and Tuesday in preparation.

Members of the union Unite have voted to reject an offer Heathrow officials said provided a 7.3% pay increase over 2½ years.

The union says it is focused on disparities between workers doing the same jobs and an "unacceptable" pay gap between workers and Heathrow CEO John Holland-Kaye.

Heathrow says it will remain open on strike days but security lines will likely be longer than normal. The airport advised passengers to contact airlines for updated flight information.