The Ulster Unionists have accused the DUP's Sammy Wilson of "pathetic party political point-scoring" for his attacks on Health Minister Robin Swann.
UUP leader Steve Aiken said the East Antrim MP had reached "a new low even for the DUP".
He said it was clear that Sammy Wilson had won the internal battle in his party "and is now pulling Arlene Foster's strings".
The DUP MP launched a stinging attack on the Health Minister on the BBC on Tuesday.
He accused him of not using enough resources within his department to slow transmission.
"Robin Swann would be much better concentrating on how he can improve the health service in order to deal with coronavirus rather than how he can destroy the economy in order to deal with the failings of his own department and of himself as a minister," Mr Wilson said.
Mr Aiken branded the East Antrim MP's remarks as contemptible. "This is more of the same pathetic, petty party political point-scoring from the DUP," he said.
"Sammy Wilson attempting to undermine a unionist minister in the middle of a pandemic is hitting a new low, even for the DUP.
"This is a man who was pictured on the London Underground not wearing a face covering.
"His colleagues now ignore medical and scientific advice."
Mr Aiken said the DUP had "run away" from taking the health portfolio in January.
"For an MP, Sammy Wilson is also very ill informed," he said.
"Mr Wilson should have read the Health Minister's statement to the Assembly yesterday.
"The key issue facing the health service is staffing capacity.
"There are over 5,000 vacancies across the Health and Social Care system and that's a direct result of years of underfunding by the Executive.
"It's a pity Sammy Wilson and his colleagues never did anything to resolve that instead of blundering about until the Executive collapsed." Mr Aiken continued: "If Sammy Wilson wants to talk about damage to the economy, he should speak to his DUP colleague, Economy Minister Diane Dodds.
"She is presiding over a chaotic Covid restrictions business support scheme which has failed to deliver for the vast majority of businesses which have applied for it.
"Half a billion pounds are sitting in the Executive's coffers and the DUP Economy Minister can't get support to the businesses which are pleading for it."
Meanwhile, Arlene Foster has called for a "collaborative and collective" way forward at Stormont.
She said she hoped that her party would not have to use the cross-community veto mechanism at Stormont again.
"We do not want to be in that position. We want to be in a position where we can come together collectively," she said.
"I hope we do not have to use it again. Let's have a collaborative way of working with the Health Minister."
The DUP has faced extensive criticism for using a mechanism designed to protect minority rights to block health regulations.
Speaking during a visit to St Columbanus College in Bangor, the First Minister said that while other parties complained about the use of the cross-community veto, they were the ones who had included one in the Good Friday Agreement.
She added that public health had improved due to the interim restrictions and the reproductive rate of the virus had dropped below one.
Mrs Foster said the Executive wasn't planning for the early closure of schools. "School is one of the safest places to be," she said.
"This is a crisis for our community and the economy. We have heard clearly from our businesses about the impact.
"People who lost their jobs, they have lost all purpose in their lives. They need to get that back again, to feed their families."
The DUP vetoed Mr Swann's proposal to extend Covid restrictions by a fortnight. The move was supported by all four other Executive parties.