After Macron signed them on Friday, the changes to labour law were rushed into print in the government's official gazette on Saturday.
The hasty publication, which was expected early next week, makes them officially French law.
It follows a fast-track adoption that cut short parliamentary debate, defended by the government on the grounds that they were urgently needed to tackle France's 9.6-percent unemployment rate.
The law and its introduction by executive decree are just two aspects of Macron's policy that have caused France Unbowed to accuse Macron of a "social coup d'état" aimed at imposing policies inspired right-wing former British prime minister Margaret Thatcher.
Opposition to Macron
With most other parties, including the far-right National Front, going through internal crises after this year's elections, France Unbowed has emerged as the most vocal opposition on the political plane.
Saturday's demonstration followed two protests and strikes led by the CGT trade union and has led to suspicions that Mélenchon and his supporters are trying to hijack the leadership of the opposition to Macron.
This week they made efforts to counter that fear, meeting CGT leaders and attending Thursday's demonstration.
But their former allies, the Communist Party, have shown only tepid support for the initiative, sending a delegation rather than mobilising their troops, and the CGT did not officially back it, although many of its activists appear to have turned out.
Mélenchon's former rival in the race for the French presidency, Benoît Hamon, who quit the Socialist Party to form his on 1 July Movement after the election, supported the protest, as did a number of other left-wing parties and campaign groups, with various degrees of enthusiasm.
There was some tension on the march between Mélenchon's supporters and the anarchist Black Bloc, who forced their way to the front and tore down posters and threw stones at the stage from which the France Unbowed leader was to speak on arrival at Paris's Place de la République.