Up to half a million shop workers suffer verbal abuse every day, a report by the retail union Usdaw suggests.
Shop workers face increasing verbal and physical abuse
The study found there was a 35% increase last year in swearing, sexist comments and other forms of verbal abuse from "out-of-control" shoppers.
The union surveyed 500 workers and some said they suffered depression because of the level of abuse. Others gave up their jobs because of the stress.
Usdaw is launching a campaign on Wednesday to highlight the problem.
Researchers found that verbal attacks on staff were as damaging as physical abuse.
Examples included a shop worker who was threatened when an item was not in stock and others who were abused for no apparent reason.
Usdaw General secretary John Hannett said: "Most shoppers would never think of physically assaulting a shop worker, but many seem to think it is all right to scream the most disgusting abuse.
"Our members are saying enough is enough and they will no longer tolerate vile abuse as part of their daily working lives."
About 2.7 million people work in the UK retail sector
35% increase in verbal abuse
20,000 workers were physically abused last year
Usdaw has 340,000 members
Usdaw will distribute 30,000 red cards, similar to those used by football referees to send off players, to shoppers nationwide on Wednesday.
The union hopes the cards, which have the words "Usdaw United Against Abuse Against Shop Workers", will remind shoppers to think twice before losing their temper.
"Referees can use a red card to send off players... so our members will be distributing the red card, spreading the message that anyone abusing staff can be removed from stores or even prosecuted," said Mr Hannett.
Shop workers who took part in the survey gave examples of their experiences with customers including:
- "On a daily basis customers think they can swear at you, be aggressive and be threatening."
- "Some customers seem to assume, wrongly that because someone works behind a counter they are a) stupid and b) a target for rudeness and arrogance."
- "The old adage - 'the customer is always right' - is, frankly, arrant nonsense and only encourages people to be rude and abusive."
- "I would say that the majority of customers are nice people who it is a pleasure to talk to, but there's a significant minority, of about a third, who are very unpleasant and ignorant."
- "I've worked in retail for eight years and during that time I've been sworn at and talked down to by customers, even when I was eight months pregnant."