The strike of ground staff at German flag carrier Lufthansa planned for Wednesday is expected to affect the country's major airports and thousands of passengers in what would mark yet another industrial action to hit Europe's largest economy in the past couple of weeks.

Some 25,000 staff will take part in the walkout, which will last for around 27 hours from 4 a.m. (3 a.m. GMT), the Verdi union said in a statement on Monday.

The workers are demanding a 12.5% pay increase over 12 months as well as one-off bonuses to counter inflation, it said.

The strike will affect Germany's biggest airport in Frankfurt as well as those in Munich, Hamburg, Berlin and Duesseldorf.

"There are likely to be major flight cancellations and delays," the union said.

Lufthansa said it was working on a "special flight schedule" and more than 100,000 passengers would be affected.

The airline said in a statement it had offered workers increases totaling more than 13% over the next three years, as well as the "prompt payment of significant inflation bonuses."

But the union said it deemed the offer "totally unacceptable."

"Lufthansa employees already have around 10% less in their pockets than three years ago. Despite record profits, this situation is set to worsen," said Marvin Reschinsky, Verdi's chief negotiator in wage talks for ground staff.

The strike comes as Germany faces a growing wave of social unrest in the transport sector.

Pilots with German airline Discover, a subsidiary of Lufthansa, were staging a 48-hour strike until the end of Monday.

Last week, airport security staff and public transport workers across Germany walked off the job.

And two weeks ago, train drivers staged a five-day walkout, their longest ever and the fourth time they have gone on strike since November.