A movement to shrink the average work week from five days to four has been growing in popularity across the Western world. The U.K. just launched the world’s biggest test yet of the four-day work week to evaluate whether such a move is viable.

The six-month pilot program, which started Monday, spans 70 companies — from restaurants to financial services providers, CNN said. The test of the four-day work week involves 3,300 workers who will receive their full pay for working 80% of a normal week. However, they have to maintain 100% of their normal productivity.

The program’s organizers, including the nonprofit 4 Day Week Global and the 4 Day Week UK Campaign, contend that companies are seeing a competitive advantage with reduced-hour, output-focused work.

4 Day Week Global CEO Joe O’Connor said in a statement, “As we emerge from the pandemic, more and more companies are recognizing that the new frontier for competition is quality of life, and that reduced-hour, output-focused working is the vehicle to give them a competitive edge.”

The movement is not a new one and has seen growth over the last few years, accelerated by the disruption to normal work hours, days and locations caused by the Covid pandemic. The increased flexibility workers experienced during the outbreak led to greater demand for making the accommodations permanent.

Skeptics of the shortened work week remain unconvinced. Tesla and SpaceX CEO Elon Musk, in fact, is pushing for more hours and less flexibility. Last week, Musk announced that Tesla staff needed to return to the office for a minimum of 40 hours a week or find a job elsewhere. He later tweeted that people who don’t want to commit time to working in the office “should pretend to work somewhere else.”

Iceland conducted its own tests of the four-day week between 2015 and 2019, CNN said. The pilot program, which included 2,500 public-sector workers, reportedly found zero drop in productivity and did see enhanced well-being among employees.

The new U.K. trial will cover not only the impact on productivity but also on gender equality and the environment.

A similar trial is also getting underway in the U.S. and Canada. 4 Day Week Global’s website shared a timeline for the pilot program that includes workshops, training, and a six-month trial period from October 2022 through March 2023.