In a speech at the Socialist Party's annual conference in La Rochelle, Valls said that France's work code is "so complex that it has become inefficient: curbed activity; wage earners who no longer know their rights", the Financial Times reported.
Employers, employees and their representatives all need "more latitude" to decide things for themselves, Valls said, according to the Financial Times.
However, Reuters reported that Valls' remarks were greeted by heckles and boos from "a small group of young party members" who accuse him of putting the interests of business over socialist ideals.
Valls said the government would continue with its plans, Reuters said.
"We are pressing ahead with the deep reforms our economy needs. We won't be swayed," he said, according to Reuters.
Valls said the government would lower taxes next year, with a proposed cut in income tax for households, to complement reductions that were already in place, the Financial Times said.
Nine million middle-class and working-class households are already paying reduced tax bills, with average savings of €300, Valls said, according to the Financial Times.
The reforms will not include France's 35-hour working week, Valls said, in response to comments last week by economy mister Emmanuel Macron.
"A long time ago, the left believed ... that France would be better off if people worked less. That was a wrong idea," Macron said at an annual gathering of French business leaders according to France 24.
Valls said in his speech that discussion on working hours "is closed", the Financial Times said.
Paris-based Coline Bied-Charreton of Pinsent Masons, the law firm behind Out-Law.com said: "The French labour code is regularly attacked by legal professionals for its disproportionate length and complexity. Also, employment law is a hot button in French politics, meaning that each new government wants to stamps its mark on the labour code. Consequently this code is in perpetual evolution, and legal amendments, often made in haste, do not necessarily take into account the existing complexity, which triggers additional complexity, or as it is called here, the legal layer cake or mille-feuilles législatif."
"Valls's government has been working hard to address the code, leading to significant reforms meant to simplify and shorten mandatory consultations with staff representatives. His latest declaration is no surprise in this context," Bied-Charreton said.