BERLIN -- Buses and commuter trains ground halted on Monday as public sector workers in Verdi, Germany's biggest trade and service sector union, began nationwide action to back calls for wage rises.

Aviation officials said that air traffic were delayed on Tuesday when airline workers at Frankfurt and Munich airports were due to stage "warning strikes" to underline their calls for a wage rise of at least three percent, Reuters reported.

Commuter traffic in many German cities was disrupted on Monday as bus and train drivers began temporary stoppages, while garbage went uncollected as sanitation workers staged walkouts two days before wage rounds are due to continue.

Police in Munich said morning commuter traffic had been hit when public sector workers began a 24-hour strike but major delays were avoided.

Verdi and the DBB civil servants union are seeking a pay rise of more than three percent for public sector workers, who number more than four million.

Their government employers, facing rising debt and falling growth, want a wage freeze.

The last all-out public sector strike in Germany was in 1992, when uncollected rubbish, undelivered post and patchy transport caused chaos.

Unions and employers meet for the next official wage round today. Verdi said it would ballot its members on all-out strike action in January if no progress was made.

"Public sector wages have fallen way behind those in the private sector. This shows are calls are justified," said Susanne Stumpenhusen, a Verdi leader for the Berlin-Brandenburg region.

Around 2,000 security personnel, ground crew and fire fighters at Germany's main airport, Frankfurt, stopped work early on Tuesday and airport operator Fraport expected delays.

Airline Lufthansa AG criticized the planned stoppages and said it would most likely hit domestic traffic.

"Please avoid millions in damages and terrible restrictions on holiday traffic. Consider that Lufthansa will be the biggest casualty of this industrial action even though it's not involved in the wage round," Lufthansa said in a letter to the union.

Last week around 40,000 German public sector workers marched through Berlin to support their wage rise call.

Interior Minister Otto Schily said he was optimistic of a deal before Christmas, but said the unions had to take into account that public coffers were empty and further tax rises could not be considered.