Heathrow faces the threat of multiple strikes by baggage and freight handlers ahead of the Easter holiday long weekend.
A series of walkouts by Unite union members are set to take place over six days between March 14 and April 9.
Thousands of passengers could be without their baggage with the action potentially impacting air travel, as well as affecting International Airline Group freight services, the union warned.
Eighty workers at Dutch logistics firm Vanderlande are in dispute with the company, which operates the Terminal 3 luggage belt as well as transporting passenger baggage to and from One World alliance, Virgin Atlantic and Emirates aircraft.
The company is also responsible for loading freight on and off IAG aircraft, including British Airways, Air Lingus and Iberia.
Unite members voted by 88.6% for strike action in a ballot with 90.9% turnout following a breakdown in industrial relations after staff rejected a 2.5% pay offer in August.
The dispute was on the verge of being resolved after talks mediated by the conciliation service Acas in October.
After increasing the pay offer to 3.2%, the company would not accept that a recognition deal with Unite applied to employees that had recently joined the firm, who would not receive the pay increase, according to the union.
Unite regional co-ordinating officer Wayne King said: “Unite urges Vanderlande to rethink its position and approach to staff and engage with the union before the strikes commence.
“It is possible to avoid a shutdown if the firm stops trying to split the workforce and tables a sensible pay offer for all our hardworking members.”
The announcement of the Vanderlande strike follows a strike which began on Monday by specialist baggage handlers who locate lost luggage working for Global Baggage Solutions.
Travel Weekly has approached both companies for comment.