Security guards have been told not to intervene if they see someone shoplifting in a store, for fear they may get hurt or have their licence revoked.
Union bosses instructed their members to 'watch, report and be an expert witness for police', but not to put themselves at risk for the benefit of 'those who may not support you afterwards'.
Daniel Garnham, general secretary of the union Security Industry Federation (SIF), said he was clarifying advice in the face of 'the growing level of shoplifting and violence', and increased 'confusion' over how staff are expected to act.
He said that security workers were confronted by 'different rules in different places', blaming the lack of a 'joined-up approach' between the regulator, employers and clients.
The intervention comes in the wake of several high-profile cases of shopworkers being dismissed over their responses to shoplifting.
Morrisons manager Sean Egan, 46, made national headlines last week when he was sacked from the branch in Aldridge, near Walsall, where he had worked for 29 years.
He was let go because he intervened with a prolific shoplifter, continuing to engage even after the thief became aggressive and began spitting, which the company said contravened their deter-and-not-detain policy.
Waitrose shop assistant of 17 years, Walker Smith, revealed earlier this month he was sacked for tackling an Easter egg thief at the branch in Clapham Junction, South West London.
Greggs has suffered attacks in recent months, with one especially prolific shoplifter (pictured) stealing close to £2,000 worth of items from the bakery
Supermarket workers have been sacked for tackling shoplifters in breach of their employers' rules including Sean Egan, 46, who tried to stop a serial thief at Morrisons
The 54-year-old grabbed the bag from the thief, which led to a tug-of-war and the £13 bag of Lindt eggs spilling across the floor. Waitrose too has a strict policy against staff confronting shoplifters.
Meanwhile, Gavin Ramsay, 49, was sacked from Asda after 25 years' loyal service for trying to prevent a young person from getting away with a stolen bottle of alcohol.
Some supermarket bosses have publicly called for security guards to be armed with batons and pepper spray to better equip them to tackle shoplifters - but the SIF insisted this would be 'reckless' without proper preparation.
It argued this would create 'even more risk in an already confused and inconsistent system'.
Members were implored to avoid intervening with troublemakers, even if that rails against their 'instincts'.
Mr Garnham's said: 'Someone else’s stock is not more important than your safety, your career or your licence.
'We need clear national guidance on lawful intervention, better and more realistic training, proper support for workers who act in good faith, and an end to policies that leave officers exposed to violence while punishing them for trying to do their job.
'Security workers deserve clarity. They deserve consistency. Most of all, they deserve support.'
Keir Starmer has vowed to end the 'free-for-all' of shoplifting with a crackdown on retail crime with a speech at Usdaw's annual meeting today
The retail union Usdaw, which has 360,000 members, is also telling its members 'not to intervene against potentially dangerous criminals and to keep themselves safe'.
GMB, one of Britain’s largest unions representing thousands of security guards, said that 'retailers cannot expect security guards to put themselves at physical risk just to protect their bottom lines'.
The bosses' intervention came as Keir Starmer promised on Monday a crackdown on 'free-for-all' shoplifting, which has often seen offenders go unpunished.
The Prime Minister said an extra 3,000 police officers have been put on the streets to combat shop theft, and that his Government will make assaulting retail workers a specific criminal offence.
That came after Ken Murphy, CEO of Tesco, called for retail abuse to be criminalised in the Mail on Sunday in 2023, and after bakery chain Greggs began moving items behind the tills to deter shoplifters helping themselves to sandwiches.
The offence is set to be introduced in the Crime and Policing Bill but has ping-ponged between the Commons and the Lords.
Labour says it will also scrap the £200 threshold for shoplifting offences, below which the crime is a summary-only offence that can only be tried before magistrates.
This will, Starmer said, end what he called the 'shoplifter's charter', ending the impunity that shoplifters feel when they steal items worth less than this.