• The regulation, which came into force on July 1, bucks a global trend of companies exploring whether to embrace a shorter working week.
• The pro-business government of Prime Minister Kyriakos Mitsotakis has reportedly said the measure is both "worker-friendly" and "deeply growth-orientated."
• Labor unions and political analysts have sharply criticized the move.
• "All it does is provide only in limited circumstances for the option of an additional working day, as an exceptional measure," Greek Minister of Labour and Social Security Niki Kerameus told CNBC via email.

Greece has controversially introduced a six-day working week for some businesses in a bid to boost productivity and employment in the southern European country.

The regulation, which came into force on July 1, bucks a global trend of companies exploring a shorter working week.

Under the new legislation, which was passed as part of a broader set of labor laws last year, employees of private businesses that provide round-the-clock services will reportedly have the option of working an additional two hours per day or an extra eight-hour shift.

The change means a traditional 40-hour workweek could be extended to 48 hours per week for some businesses. Food service and tourism workers are not included in the six-day working week initiative.

The measure would impact two specific types of businesses: Those with continuous 24/7 operations that use rotating shifts, and those firms that operate 24 hours a day, five or six days a week, also using rotating shifts. With the latter, the additional working day option is permissible only in the case of an increased workload.

"It is important to note that this new regulation does not in any way affect the established five-day/40-hour working week mandated by Greek law, nor does it establish a new six-day working week," Greek Minister of Labour and Social Security Niki Kerameus told CNBC via email.

"All it does is provide only in limited circumstances for the option of an additional working day, as an exceptional measure. Most countries in Europe have similar provisions for exceptional additional working days. So Greece is not doing anything different," she said.

The pro-business government of Prime Minister Kyriakos Mitsotakis has said the measure is both "worker-friendly" and "deeply growth-orientated." It is designed to support employees not being sufficiently compensated for overtime work and to help crack down on the problem of undeclared labor.

Labor unions and political observers have sharply criticized the move.

Giorgos Katsambekis, a lecturer in European and international politics at the U.K.'s Loughborough University, described the Greek government's introduction of the labor law as "a major step back" for a workforce that is already working the longest hours in the European Union.

Workers in Greece work more than those in the U.S., Japan and others in the 27-member EU, according to data from the Organization for Economic Cooperation and Development.

Greek employees were found to have worked an average of 1,886 hours in 2022, more than the U.S. average of 1,811 and the EU average of 1,571.

"Greek people already work the longest hours per week in Europe. Now they may be forced to work a sixth day, after this Greek [government] decision," John O'Brennan, professor of EU Law from Maynooth University, Ireland, said via social media platform X on Monday.

"It is ridiculous, set against the move to four day weeks in most civilised countries," he added.

Greek Minister Kerameus added that these new measures protect workers "against under-declared and undeclared work and ensures fair compensation."

"Under said regulations, employees that happen to work on the additional day are entitled to a substantial increase in their daily wage, which can amount to up to 140% under specific conditions. Additionally, the law stipulates more measures to ensure the protection of workers, such as guaranteed days off, specific working hours, and safeguards against unfair dismissal," she said.

Four-day trial

A report published by think tank Autonomy earlier this year found that most companies involved in the world's largest trial of a four-day working week had made the policy permanent.

All the consulted project managers and CEOs of the companies involved in the trial said a four-day working week had a positive effect on their organization, with more than half describing the impact as "very positive."

The report found, however, that staff — in firms where the additional day off was only weakly guaranteed, or provided on the condition of meeting certain targets — had some concerns.