Trade unions said a total of 175,000 took part in the protests, the DPA reported.
Speaking in the western city of Essen, German Trade Union Confederation (DGB) leader Yasmin Fahimi criticized plans by Chancellor Friedrich Merz's government coalition in Berlin to seek reforms to working hours and pensions, and warned against cuts to social security benefits.
Under the slogan "Hard-earned! Your work. Your health. Your pension," people marched through 15 major cities. The DGB sees this as a "clear signal." At stake are secure jobs, good working conditions and the protection of workers' rights, it said.
The mass rallies are taking place against a backdrop where, in the car industry for example, many workers fear for their jobs and the already embattled coalition government is locked in a fierce struggle over the next steps in reform.
The DGB had already announced the protests back in July.
Following recent regional parliament elections in Mecklenburg-Vorpommern and Berlin - which proved disastrous for his party - Merz stated in mid-September: "The reforms must go ahead."
Pensions have been the focus of attention for weeks, whilst at the weekend a dispute over care provision flared up within the coalition.
In Nuremberg alone, the police counted between 20,000 and 25,000 people. They put the figure at 12,000 participants in Essen and 15,000 in Frankfurt. There were around 13,000 people in Hanover, 16,000 in Stuttgart, 4,500 in Freiburg and 5,500 in Berlin.
Rallies attended by thousands of people also took place in Hamburg, Kiel, Rostock, Magdeburg, Leipzig, Erfurt and Saarbrücken. In the afternoon, the DGB put the total number at around 175,000 people.