The bitter dispute involving thousands of British Airways cabin crew will take another twist when union leaders will hear whether they can go ahead with a series of planned strikes.
A wave of five-day walkouts was due to start this week but BA was granted an injunction against the Unite union, granting a reprieve to the airline's passengers.
The union lodged an appeal, with the decision due to be announced this morning.
If the judgment goes against Unite, the union is expected to hold another ballot of thousands of cabin crew in the long-running row over pay, jobs and working conditions. But if the judges accept Unite's appeal, the strikes will go ahead, probably from next week.
Unite originally announced four five-day stoppages from May 18-22 inclusive, then from May 24-28, May 30-June 3 and June 5-9, the last strike ending just days before the start of the football World Cup in South Africa.
It is likely that Unite will resume its planned strikes from next Monday if it wins the court ruling.
British Airways ran a full long-haul service from Heathrow on Wednesday as it waited for the court decision, saying its global operation started well.
Unite members will travel in an open top double decker bus through the City of London shortly before the court decision is announced, and the union said it wanted to warn the airline's top investors that BA chief executive Willie Walsh was playing "fast and loose" with their money.
A representative of the cabin crew will deliver a letter from Unite's joint general secretaries urging the investors to use their influence to bring stability back to the airline.
Unite claimed that Monday's High Court injunction called into question whether workers still had the right to take action.