By Martin Shankleman
Employment Correspondent, BBC News
The toilet break policy is to avoid disruption, the firm says.
A meat company supplying Tesco has been accused of "Dickensian employment practices" by making workers clock off when they go the toilet.
The Unite union is now calling on Tesco to intervene to stamp out the practice at Dumfriesshire-based Brown Brothers.
One worker said staff felt "angry" that time spent in the toilet was not included in their working week.
The firm said the policy was part of a deal agreed with workers and unions to ensure production ran smoothly.
The employee, who asked not to be named, told the BBC that a single toilet break could take up to 10 minutes.
"We have to clock out, take off our wellies, overalls and hairnets, we have to run up stairs, have to come back in get dressed again," she said.
Office staff and managers were exempt from their rules, she claimed.
Brown Brothers' managing director Martin Godfrey agreed that staff were not paid for toilet breaks, but said it was part of special pay deal agreed with the workers and union to ensure the smooth running of the production line.
Unscheduled toilet breaks could cause significant disruption, especially as staff wore protective clothes, he said.
"Is it not better to come up with a deal to discourage that from happening?".
Staff received extra money as part of the pay deal which was aimed at focusing toilet breaks at set times of the day, he said.
"They have already been paid to manage their own lavatorial affairs."
A spokesman for Unite said Tesco should take responsibility for the working practice.
"They pick their suppliers, and sign up to ethical codes, we think they should intervene and stop it," the spokesman said.
A Tesco spokesman said they took issues of labour standards very seriously and require suppliers to meet those standards.
The supermarket did not plan to intervene, but "the position might change", he added.
In my time I have had to work in a call centre - the modern equivalent of the workhouse. Any time we spent away from our phones was logged. It was not deducted from our pay but we could be sacked for exceeding a certain threshold. Dickensian employment practices are rife in today's Britain.
A similar thing happened to my husband. He worked for a major insurance company, then based in London. He was told he had to get to his office early enough to take his toilet break before his official start time. With the times of trains this meant he had to arrive at work half an hour before his start time.
Sue Overall, Epsom, Surrey
I work for a large haulage company and was hauled before my supervisor as I had stopped for unauthorised breaks of... wait for it... 2 mins, 3mins, 7 mins and 8 mins. Bosses are obsessed with people stopping work for any reason. It's also a great way of putting presssure on other workers who hear about these instances of harassment and serves the purpose of keeping everyone in the workforce in check.
Michael Kilgannon, Hemel Hempstead
I am a manager in a food processing unit and have first hand experience of workers planning their toilet breaks to avoid jobs they don't like doing. I have also seen people hide newspapers so they can sit on the loo for 20 mins in work time.
As a manager who needs 20 people on a line, I cannot stop the line every time someone needs the loo.I tell people that I'll never stop people from going to the loo, but I do threaten to refer persistant offenders to the company nurse if they insist they can't hold on until a convenient time.
I worked for an IT support team and took a toilet break. It could only have been 3 minutes. When I got back I saw that I'd missed a phone call and in the interim period (3 mins) the matter had been escalated to senior management and there was hell to pay. What was I supposed to do? This company was French and I'm pleased to say that I don't work for them any more. When did we all lose our common sense?
Steve Cahill, Sandy, England
This is common practice in most call centres! Worst of all, if you are gone for more than a few minutes you are interrogated as to why you've taken so long.
Why cant you just wait to use the toilet in one of your breaks? I don't see the problem with this, I worked in a factory doing 12 hour shifts I always used the toilet during breaks.
In my workplace many of the staff nip off to the toilet for 15-20 minutes and more at a time (to speak on the mobile, read and even take a nap!). When you have 50 staff and many of them doing this how many hours of work are being lost? Not only that but the firm struck a deal for staff to receive extra money to focus toilet breaks at certain times of the day. And of course you would be expected to take off your overalls when going to the toilet! Especially in a company dealing with foods.