Workers at two airports in Berlin on Monday said they would extend a walkout over pay that has grounded almost all flights out of the German capital.
Service workers' union Verdi on Sunday said it would call ground personnel out on strike just two days after their last walkout on Friday.
The stoppage was slated to begin at 4:00 am (0300 GMT) Monday and last until 5:00 am (0400 GMT) Tuesday, affecting some 660 flights.
But the union said in a statement Monday that it now plans to extend the walkout until early Wednesday morning.
Some 195 flights were cancelled at Schoenefeld, while 465 were affected at Tegel, airport operator FBB told AFP Monday.
"We ask all passengers to contact their airline and find out the status of their flight before setting off," said FBB spokesman Daniel Tolksdorf.
Verdi wants higher pay for around 2,000 ground staff in Berlin, including those registering passengers and loading baggage.
Employees walked out twice in February as the union ratcheted up pressure.