Further strikes are set to take place this weekend
British Airways cabin crew who took part in the Unite union's three-day strike will forfeit their travel perks permanently, the company has confirmed.
Staff are eligible for free and heavily discounted flights, depending on how long they have worked for BA.
Unite condemned the move, confirmed in a letter to strikers, as "vindictive" and said it would challenge it.
Meanwhile, the UK Supreme Court has sent a dispute over BA pilots' holiday pay to the European Court of Justice.
The striking staff had been warned by BA's chief executive Willie Walsh before they took part in the action on Saturday, Sunday and Monday that they were at risk of losing the perks.
Hundreds of crew members are believed to be affected.
A BA spokesman said: "Staff travel offers heavily discounted travel to employees. This is a non-contractual perk that the company can withdraw at its discretion.
"The industrial action impacted on our operation and our customers and we will undoubtedly suffer additional costs and further losses as a result."
A spokesman for Unite said: "This is the clearest possible example of BA's bullying and contemptuous approach to its employees. Cabin crew showed last weekend that they will not be intimidated.
"Unite will challenge this vindictive move in whatever way seems appropriate."
The joint leader of Unite, Tony Woodley, had told strikers on Monday that he believed the long-established discounts were not just a perk but "custom and practice".
But British Airways said it has lost at least £21m because of the action. A further four-day strike is set to begin this Saturday.
During prime minister's questions, Gordon Brown repeated his plea for staff to return to work. He had been requested to do so by Conservative MP, Brooks Newmark.
The strike action is the latest episode in a long-running dispute over changes to pay and conditions by BA that union Unite claims are being unfairly imposed on its members.
Workers are particularly angry that last November BA reduced the number of crew on long-haul flights and is introducing a two-year pay freeze from 2010.
Strikers received a letter telling them would lose their perks
The airline also proposed new contracts with lower pay for fresh recruits.
Meanwhile, a dispute between the British Airline Pilots' Association (Balpa) and British Airways over holiday pay is continuing to play out in the courts.
The association wants BA pilots' holiday pay to be based on what they actually earn. Currently it is based on their basic pay without any allowances included.
But BA is resisting the claim, which could lead to more than 3,000 of its pilots each getting an average of £600 a year more.
Since this is a test case, this could potentially affect up to 12,000 pilots and cabin crew working for BA and other airlines.
The Supreme Court has decided the issue of paid annual leave comes under European law and so have sent it on to the European courts.
BA has always maintained that its holiday pay arrangements are "generous", and comply with legislative requirements.