A union has warned British Airways not to victimise staff who took part in a wildcat strike last week.
The dispute caused major disruption at Heathrow
The Transport & General Workers' Union (T&G) warned it would support "legal industrial action" in a row over job cuts at catering firm Gate Gourmet.
BA is investigating whether ground staff were bullied into taking part in the unofficial strike in support of 670 workers sacked by the caterer.
BA also said it will not pay staff who walked out as they had broken the law.
BBC labour affairs correspondent Stephen Cape says workers who are found to have breached the airline's policies could now face a warning or dismissal.
The airline has also launched a confidential hotline for staff to report any concerns.
The warning from the T&G came after BA chief executive Sir Rod Eddington dubbed the action "outrageous" and "a body blow that defies belief" in an open letter to staff.
T&G General Secretary Tony Woodley said that while the union recognised the action was unlawful, he was "disappointed" at Sir Rod's comments which had caused "great resentment" among its members.
Mr Woodley added that there were many links between Gate Gourmet and BA workers at Heathrow as many of the caterer's staff were previously employed when BA ran its own catering operation.
"Would it not be a bitter irony if, in the same family, in the same household, that a husband was now victimised for exercising his conscience by standing up for his wife - the former a British Airways employee, and the latter employed by Gate Gourmet?" he said.
"Were that to happen, this union would support legal industrial action to protect victimised members."
Last week's action forced BA to shut down operations at Heathrow - resulting in the cancellation of 700 flights, causing disruption to the journeys of 100,000 travellers and costing BA more than £30m.
The airline is still unable to offer a full food service and does not expect to be able to offer hot in-flight meals until some time next week.
Gate Gourmet welcomed BA's investigation into the cause of the wildcat strike by BA workers.
"Gate Gourmet have always taken a very dim view of illegal action, but we must accept that often people are taken up in the emotion of the situation or feel intimidated into taking illegal action," said the company's UK managing director Eric Born.
The caterer has also said it is looking into T&G claims of improper corporate activity and "major health and safety concerns" - Gate Gourmet said it did not believe there had been any wrongdoing and wanted to "make sure that was the case".