Gate Gourmet provides onboard meals for British Airways flights. The workers' union said the company had fired 800 workers on Wednesday after an unofficial strike. The company said 667 workers had been dismissed.
BA baggage handlers and loaders represented by the same union as catering staff - the Transport and General Workers Union - stopped work in sympathy with their colleagues.
Some Gate Gourmet staff were astounded at the scale of disruption.
''I didn't expect the BA staff to join us, but we are very happy about it,'' said Gary Mullins, a loader for the company.
''We don't wish to cause them any more (aggravation) than we have to,'' he said of the passengers. ''But it's something that has to be done.''
Gate Gourmet, which is undertaking restructuring amid financial losses, said it was trying to resolve the dispute. The company, owned by U.S.-based Texas Pacific Group, reported a loss of 23 million pounds ($41.25 million) in the last fiscal year, and was expecting a 25 million pound ($44.84 million) loss for the current year.
This is the third consecutive year that BA has suffered a disruption at the height of the summer holiday season. Last August, thousands of disgruntled vacationers were stranded at Heathrow after the airline canceled scores of flights because of staff shortages and technical hitches.
In July 2003, an unofficial walkout by several hundred check-in staff disrupted thousands of passengers and cost BA tens of millions of dollars.
Henk Potts, an analyst at Barclays Stockbrokers said the latest dispute could cost the airline 10 million pounds ($18 million) a day.
In its last fiscal year, which ended in March, British Airways PLC earned 251 million pounds, up from 130 million pounds in the previous year. Full-year revenue rose 3.3 percent to 7.8 billion pounds.
BA's U.S. shares fell 14 cents to $52.69 in afternoon trading on the New York Stock Exchange.