The supermarket has been the victim of cases at a store in Bridgend, a Tesco Extra in Cardiff and a depot in Magor, Monmouthshire.
A staff member at the Bridgend store said there had been 40 confirmed cases since Christmas, with 140 workers isolated at one point.
The worker added that shoppers were ignoring social distancing during the chaotic festive period, Wales Online reports.
Bridgend currently has the second highest coronavirus infection rate in Wales, with 894.3 cases per 100,000 population.
A worker at the Cowbridge Road store in Bridgend said: ‘There have been at least 40 confirmed cases since Christmas.
Are you a supermarket worker worried about catching coronavirus? Email [email protected]
“About a third of the workforce isolates itself through contact with someone or through tracking and traceability.
“The staff are scared, absolutely scared. Due to the number of people in the store, Tesco has now reduced the number of people who can enter, but before Christmas there was no authority.
“There were people who said they didn’t let their kids go to school because of the risk of Covid, but then went shopping with the whole family. ”
The employee said he could not keep a safe distance from other people in the store because customers were not following guidelines.
They added that most buyers also do not wear their masks properly.
“We’re all just scared and we wonder who’s going to get it next,” the worker said.
“And if we catch it, who will we report it to.” Unfortunately, we need our jobs, so we have no choice. ”
The employee said the cases were “storewide in every department” and the home shopping department had been hit hard: “There are people working on home orders and customers just walking in. next to them.
“The number of orders entering the [website] are just as much as before Christmas. There could be customers with coronavirus who handle the items in the store and hand them over, and then those same items are delivered to the people at home.
“There are so many customers in the store, it was only a matter of time. The store still employs people because the normal staff are dropping like flies. ”
Tesco is not the only supermarket facing such problems. A Welsh Lidl store worker told a very similar story.
“I don’t just worry about myself, I worry about my coworkers,” the employee said.
“Customers don’t wear masks, so we’re the ones who are mistreated when we ask them to do so because they don’t wear exemption badges. There are marks on the floor, but no one is following them and there is no one at the door checking the numbers. It’s like a free for all.
“After 6 pm, we might as well be unlicensed. No one comes for essential purchases and they come as a group on a family day out. I have been working in supermarkets for over a decade, but looking to get out like I can’t get by anymore. ”
A Tesco spokeswoman said: “A number of colleagues at our distribution center Bridgend Extra and Magor are on sick leave due to Covid-19. Their close contacts have been informed.
“The safety of our colleagues, customers and suppliers remains our number one priority and we follow all government guidelines and work with local public health authorities.
“We have extensive measures in place in all of our stores and distribution centers to ensure the safety of everyone, including protective screens at each checkout, a signal light system at the entrance to our store for monitor numbers, social signage and regular cleaning. ”