Carers danced together and shared a microphone during a pub DJ visit at the home where they worked.
The two-metre social distancing rule was ignored as staff swayed their arms and boogied at the Clap for Carers event.
A video shows the group get up close other while on duty outside Carnbroe Care Centre in Coatbridge.
Footage emerged after Andy Cumming was brought in to entertain residents, the Daily Record reports.
Workers were filmed linked together and dancing, without wearing PPE equipment.
NHS Lanarkshire was tipped off about the incident by the Care Inspectorate, who has "vigorously reinforced" coronavirus guidelines with the home's management.
In the 33-minute video, Mr Cumming, regularly booked to entertain pub punters, is seen bending down next to staff and putting a microphone to their mouths, encouraging them to sing Petula Clark hit Sailor.
Infectious diseases expert Professor Hugh Pennington criticised the event.
He said the high-jinks heightened the risk of Covid-19 entering the home and that singing into a shared microphone "significantly increases the likelihood" of transmitting the virus.
The emeritus professor of bacteriology at the University of Aberdeen added: "One way the virus gets into a care home is staff taking the virus in.
"They can infect residents as part of their normal daily work without realising what has happened because they haven't got any symptoms.
"The closeness of the staff flouted social distancing rules between individuals handsomely, and singing - with its vigorous expulsion of breath from the mouth - significantly increases the likelihood of virus transmission.
"In a sense, they're breaking the rules, they shouldn't be as close to one another.
"Singing is a risk factor for transmitting the virus."
National Records of Scotland figures show there have been 1,623 coronavirus-related deaths in care homes - 46 per cent of all fatalities linked to the killer bug in Scotland.
Official statistics reveal 651 of adult care homes - 60 per cent - have reported at least one suspected Covid-19 case to the Care Inspectorate since the start of the epidemic.
Miles Briggs MSP, the Scottish Conservative shadow health secretary, said: "Even though the intentions behind this were good, it was clearly a terrible decision.
"It's hard enough to keep this deadly infection out of care homes.
"Having strangers mingle so closely with the staff will only have heightened the chances of Covid-19 spreading within the home."
Following the performance on April 24, Carnbroe Care Centre used Facebook to thank a resident's family for organising the event.
It wrote: "Another huge thank you for organising DJ Andy Cumming to come and perform for the residents and staff at the care home last night.
"Everyone had a great night and cannot thank you all enough for your kind gesture."
The home, which is owned by the Alpha Care Management Services, provides nursing care for up to 74 elderly residents and those suffering from dementia.
A spokesman said the facility had been unaffected by Covid-19 and none of its staff or residents had been infected by the illness.
He added: "Our priority is always the wellbeing of our residents and giving them the best possible care experience.
"We have organised a number of social events to allow residents to enjoy themselves during what is an extremely difficult time for everyone.
"The event in question was organised at short notice by the family of a resident and took place in the car park of the home.
"We acknowledge that the appropriate social distancing measures and use of PPE - followed vigilantly within the confines of the home since we introduced them before government guidance was issued - were not fully implemented on this occasion."
Mr Cumming said: "I'm sorry if any rules were broken, although the mics were consistently wiped with sterilisers.
"I was under the impression the carers worked closely together in the home, so there wouldn't be much of a problem.
"I was unaware that some people had been videoing it on their phones.
"No PPE advice was given and, after you have made me aware, I do admit that the set was irresponsible."
A Scottish Government spokeswoman said: "We appreciate that the measures in place can be frustrating for people, but they are absolutely necessary to stop the spread of the virus, protect people who are vulnerable and save lives.
"Gatherings are discouraged unless people are members of the same household or where it is essential for work purposes, and physical distancing measures should be adhered to at all times."
A Care Inspectorate spokesman added: "We are in contact with this care home and have discussed this with management.
"We have vigorously reinforced the need for physical distancing and continued vigilance to keep residents safe, and have noted that the matter has also been reported to Public Health colleagues."
North Lanarkshire Council confirmed they are aware of the video and have discussed it with the Care Inspectorate.
