Spain's leftist government began negotiations Thursday to reduce the legal workweek from 40 to 37.5 hours, sparking resistance from business groups as it tries to live up to a political promise.

The measure would concern about 12 million people, and was part of the agreement Prime Minister Pedro Sanchez reached to bring far-left Movimiento Sumar party into his coalition that took office late last year.

"Cutting working hours not only means working less, but working better," labour minister and Sumar head Yolanda Diaz said on social media platform X as talks got underway with labour unions and business associations.

The Spanish "deserve a work rhythm that allows them to live," said Diaz, adding that the workweek is unchanged in 40 years despite major gains in productivity.

The government is proposing a two-step reduction, going down to 38.5 hours in 2024 and 37.5 hours in 2025, without loss of salary.

Spain's two main unions, the UGT and CCOO, have expressed their approval, unlike business leaders who say it would endanger the viability of some parts of the economy.

"Not all sectors are alike," Antonio Garamendi, head of the CEOE business lobby said during a meeting earlier this week, adding that talks should be held branch by branch.

Diaz has said that she wants an accord with the blessing of both unions and business, but hasn't rejected the possibility of only negotiating with the unions as she did earlier in January when raising the minimum wage.

To get the law through, the government will also a difficult task winning over other members of its coalition, especially Basque and Catalan regionalist parties that have closer ties to the business world.