Nicoley Baublies, the head of the UFO union, said in an interview on German public television that the strike could go for 24 hours on Friday and could affect the entire country.

Strikes on Tuesday caused cancellations and delays at Germany's three biggest airports - Frankfurt, Berlin-Tegel, and Munich. Of the company's roughly 1,800 daily flights around the world, more than 340 were cancelled on Tuesday, the company said.

Last Friday, an eight-hour strike was largely limited to Frankfurt, but UFO continued to raise the stakes by warning of a nation-wide strike on Friday.

"We've proved that we can strike," Baublies said in Munich on Tuesday when he announced that the next walkout was timed to start at midnight Friday morning, last 24 hours, and affect all of Lufhansa's 16 airport locations in Germany.

The union said Friday's strikes could be avoided if Lufthansa agreed to arbitration without preconditions.

UFO is demanding a 5 percent pay raise backdated to January of this year. Lufthansa has countered with 3.5 percent.

"We don't see the need for arbitration," said a Lufthansa spokesperson on Tuesday, "because an offer is already on the table, and it's a good starting point for further negotiation."

mz/ipj (dpa, Reuters)