The measures – designed to give more flexibility to employers, who have long complained of red tape strangling the French economy, while offering more protection to employees – were adopted by an overwhelming majority on Tuesday.
Three of France's union confederations and the employers federation signed off on the reforms in January, and the package was then sent to the French cabinet for ratification and on to the lower house National Assembly. It has yet to go to the Senate.
But two other powerful unions – CGT and Force Ouvriere (FO) – are against it and thousands protested the reforms across France Tuesday, with many converging on the National Assembly as the deal was adopted.
Far-left leader Jean-Luc Melenchon, who was part of the protest, said the reforms were "extremely cruel and unfair for workers".
"They are having a hard time convincing us that it will help respond to the set objective of creating jobs," added Thierry Lepaon, head of the CGT.
The reforms stipulate for instance that if a firm is going through a tough time, employers would be able to reduce workers' salaries or their working hours for a fixed period in exchange for a guarantee that no one will be laid off.
French authorities would also have less leeway to block job cuts when companies hit difficulties, provided severance deals are agreed with employees.
But all employers would also have to provide complementary health insurance on top of the state's social security net.
Critics have long complained that high wages and reduced working hours enjoyed by some of the French workforce – particularly those on permanent contracts – discourage investment in the country.
In February, the head of US tyremaker Titan sparked an uproar in France by mocking French workers for putting in only "three hours" a day and saying it would be "stupid" to invest in the country.
Romain Chiss, a Paris-based lawyer specialised in labour law, said the agreement was a significant step forward.
"It's a very balanced agreement, which seen from the outside will send a positive sign," he said.