Fast-food giant McDonald's has been reported to the Commission for Racial Equality (CRE) after a Manchester branch ordered staff to speak English at all times - even when they are on their breaks.
A notice posted in the staff room of the company-owned restaurant in Manchester's Trafford Centre shopping complex threatened staff with disciplinary action if they spoke foreign languages at any time.
It claimed these instructions came from head office.
But McDonald's denied this was company policy. It said the notice, which has now been taken down, was a one-off case and had been written by a junior manager using unapproved wording.
The chain, which has a multi-ethnic workforce, added: "Staff are encouraged to speak English when working and when liaising with customers. Outside of those times, such as in the staff room and on breaks, we of course respect their right to converse in whatever language they choose."
The CRE, which is looking into the complaint, agreed that it was reasonable to ask staff to speak English when serving customers, but added that "there may be a different view of applying it in the staff room".
Michael Bradshaw, an associate at law firm Charles Russell, said the case highlighted the importance of train-ing managers and supervisors in equality law.
This, he argued, would give the company some protection from prosecution when company policy was mistakenly or over-zealously interpreted locally, so long as it dealt quickly with complaints.
Bradshaw warned that a blanket ban on using foreign languages in public places between staff or with customers whose first language was not English represented a grey area that could be construed as racism.
A company's liability for similar slip-ups by franchisees would depend on how independently the franchisee operated.