Workers at Germany's national postal service, Deutsche Post, began warning strikes on Sunday night and early Monday after talks between the company and the Ver.di service industry union failed to produce an agreement.

Workers in the major cities Duisburg, Wiesbaden and Hamburg temporarily stopped working in the first step of what could become the next major strike in Germany after massive disruptions in recent months to the national railway and public transportation in the federal capital Berlin.

"Employees and customers of company this healthy have a right to expect it to refrain from trying to maximize profits at their expense," said Ver.di representative Wolfgang Abel. A Ver.di spokesperson said work stoppages were also planned in other parts of Germany.

In a statement, Ver.di blamed Deutsche Post's board for the warning strikes, saying it alone bore responsibility for the fact that tens of thousands of post customers in the populous Ruhr and Lower-Rhine regions of western Germany would not receive any mail on Monday.

Letter carriers also laid down their bags and parked their bikes in eastern parts of the state of Hesse and the northern states of Hamburg and Schleswig-Holstein. Further warning strikes are expected this week, and millions of households across Germany are likely to be hit.

After two days of negotiations, Deutsche Post and Ver.di were unable to come to an agreement about job protection guarantees, working hours and wages for the company's 130,000 workers. The union wants to vote by the end of April on a full-fledged and unlimited strike that would start on May 2 in order to force the former postal monopoly to its knees.

Under Deutsche Post's current offer, workers would be given a wage increase of 5.5 percent in exchange for extending the workweek by 30 minutes and providing a guaranty there would be no layoffs prior to June 30, 2011.

However, Ver.di claims there are hidden costs in the proposal, saying Deutsche Post actually intends to increase the workweek by 2.5 hours by adding the 30 minutes and cutting employee break times. The union argues that would result in the loss of 12,500 jobs. The company, in turn, accused the union of making the figures up.

However, Deutsche Post appeared prepared on Monday to make some further concessions. The standing offer, personnel chief Walter Scheurle told the Munich daily Süddeutsche Zeitung, "is not the last word from Post."