ACTU president Michele O'Neil on Saturday called on the grocery retailer to take action after Teys Australia abattoir workers in South Australia were directed to wear coloured hairnets to indicate their infection status.
"Woolworths is turning a blind eye to the exploitation of workers by a major food supplier in the supermarket's supply chain ... who are forcing workers to continue turning up for work even though they are infected," she said in a statement.
Ms O'Neil said the practice was demeaning but staff were reticent to take a stand.
However Woolworths said on Sunday it had been assured no COVID-positive workers would be allowed back at the plant when it reopened for business on Monday.
"We expect all of our suppliers to adhere to the COVID safety protocols set by their relevant state authorities," a spokeswoman for the retailer told AAP.
"When work resumes on Monday, Teys has advised that there will be no COVID-positive team members working on site within their seven-day isolation period as required by SA Health."
She said Teys had indicated it had acted with the approval of authorities to implement "an exceptional temporary arrangement for several days last week" in response to circumstances at the plant.
However those measures were no longer in place.
"We were not involved in the decision to introduce these temporary measures and we are looking into the issues raised to ensure the labour standards we set for our suppliers have been met," the Woolworths spokeswoman said.
It's understood health officials approved the exceptional arrangements at the abattoir between Monday and Thursday last week to avoid significant loss of unprocessed beef.
