Organisers claimed the day of action had been a success despite divisions in trade union ranks and promised new protests the day before the government meets to finally agree the changes.
"For a first, it's good first," Philippe Martinez of the CGT, which called for the protests with the support of some other radical trade and students' unions, declared.
The interior ministry put the number of protesters in towns and cities across France at 223,000, while the CGT claimed 400,000 had joined the demonstrations.
There were some clashes between groups of protesters and police in Paris, Marseille and the western city of Nantes, with four arrests in the capital.
Tuesday's demonstrations mobilised nearly as many as the first demonstrations against the previous, Socialist government's labour reform in 2016, despite the fact that the unions were more united then.
Government sticks to its guns
Noting "a certain level of mobilisation", government spokesman Christophe Castaner promised to "listen to the fears" of the reform's opponents and come up with a response to them.
But he pointed out that the national leadership of two major union federations, the CFDT and Force Ouvrière, had not backed the protests "because they are waiting to see the text, which is not the horror some people are making it out to be".
Prime Minister Edouard Philippe also said he was listening to the demonstrators' concerns, adding that "there are a certain number of elements still to be discussed".
But the ordonnances - a form of decree that limits parliamentary debate - will go to the cabinet on 22 September because the government has a mandate for them, he said.
"Where's the democracy if the parliamentary majority is systematically challenged?" he asked on France 2 TV.