Workers in global supply chains should not be asked to work more than 60 hours per week, according to a revised clause in the labour code drawn up by an alliance of companies that includes Tesco, Asda, M&S, Next, New Look, Primark and Zara.

The Ethical Trading Initiative (ETI) says the changes should make its labour code clearer to understand and implement - as well as helping companies better understand and uphold laws and international standards.

The new wording makes clear that workers should be asked to work no more than 60 hours per week, unless there are exceptional circumstances. Predictable seasonal peaks are not classed as exceptional circumstances - but unexpected production peaks, accidents or emergencies are.

It also makes it clear that overtime should be used responsibly with workers' wellbeing the first priority.

Workers should receive an overtime premium that is 125% of their normal hourly wage. And they should have at least one day off in every seven days, no matter where in the world they work.

The provision had previously said: "Workers shall not on a regular basis be required to work in excess of 48 hours per week. Overtime should not exceed 12 hours per week."

"We recognise that some workers will want to increase their income by maximising their hours, particularly in low paid jobs," explains ETI director Peter McAllister.

"But it is important that there are limits and that overtime is managed in accordance with laws and labour rights standards. Working excessive hours can reduce productivity and quality but more worryingly, it can increase the risk of accidents and cause health problems."

The ETI Base Code is a nine-point code used by companies and suppliers around the world. Largely drawn from International Labour Organisation (ILO) conventions, it covers core workers'

rights including health and safety, working hours and freedom of association.

ETI is advising companies and suppliers to become familiar with the revised wording and start putting in place any necessary changes over the coming months. Audits will begin using the revised wording from December 2014.

A suite of materials has also been put together to help companies plan how they will implement the revised working hours wording. This includes a video, an interpretation note, a guidance document and a half-day training course for UK-based companies and suppliers.

An e-learning module is also being developed to support international companies and suppliers.