DUP MP Sammy Wilson has been criticised for describing NI's health minister as "a poodle".
In a tweet on Thursday morning, Mr Wilson accused Robin Swann of acting like a "poodle for the unaccountable chief medical officer".
It was in response to what he considers Mr Swann's "cautious" approach to the reopening of schools.
But responding on Twitter, Mr Swann said he "would always have considered himself more of a Jack Russell".
On the reopening of schools – the Health Minister needs to show some political independence and start acting as a politician rather than a poodle for the unaccountable Chief Medical Officer.— Sammy Wilson MP (@eastantrimmp) February 25, 2021
DUP leader and First Minister Arlene Foster said "sometimes tweets would be better to be typed out, and then deleted".
"I know people are frustrated, I know people are angry. It is certainly not language I would have used," she said at the NI Executive's coronavirus briefing on Thursday.
"But I think there is a genuine desire to have a debate about the need to get young people back to school."
'A bit unedifying'
Deputy First Minister Michelle O'Neill said the remark was "disgraceful".
"You have to have robust exchange at times, however, there's no room for being disrespectful," she added.
Earlier, her Sinn Féin assembly colleague Pat Sheehan described Mr Wilson's comments as "a bit unedifying".
"We've had clear advice from the chief medical officer about how much he expects R to rise if all schools open in their entirety," he told BBC Radio Ulster's Talkback programme.
"It beggars belief that the DUP still want to hitch their wagon to Boris Johnson."
If I had to chose, I would have always considered myself more of a Jack Russell. pic.twitter.com/uA19OaDP0N— Robin Swann MLA #StopCovidNI (@RobinSwannMoH) February 25, 2021
Mr Sheehan added that "rather than be hostages to dates on the calendar", the executive should be cautious and only make gradual, incremental moves to ease lockdown based on data from health officials.
Mr Sheehan said to open up sectors now would be a "big gamble" and would risk undoing progress made so far to reduce the spread of infection.
'Unhelpful and insulting'
SDLP MLA Daniel McCrossan said no-one should be undermining scientific evidence at what is a "critical stage" in the response to Covid-19.
He described Mr Wilson's tweet as "unhelpful, thoughtless and frankly insulting" and called on DUP leader Arlene Foster to sanction him for the remarks.
Mr McCrossan's party colleague, Mid-Ulster MLA Patsy McGlone, responded to the tweet with a picture of the East Antrim MP travelling on London public transport without a mask.
"Your advice and example has been truly invaluable throughout this pandemic," he said.
Former deputy lord mayor of Belfast, Alliance councillor Peter McReynolds, tweeted: "The health minister needs to listen to the science during a public health emergency.
"You [Sammy Wilson] may enjoy ignoring medical and scientific advice but people in positions of leadership during a pandemic do not."
'Second class citizens'
All schools in England are to reopen on 8 March.
Under the current timetable, only pre-school, nursery and pupils in primaries one to three will return to classrooms in Northern Ireland on 8 March. After two weeks, they will resume remote learning so older pupils in years 12 to 14 can go back to school.
Conflicting approaches to the reopening of NI schools has been causing rising tension within the Stormont executive and wider political sphere.
On Thursday, the education minister said his preferred option had been a full return to school on 8 March.
Peter Weir said he did not want NI to be "out of sync" with the rest of the UK or "second-class citizens".
He said NI was in a similar position to England and it was therefore "hard to square the circle of Michael McBride and Chris Whitty being on the same page," considering the medical advice on reopening schools was different in the two jurisdictions.
It is not expected to include indicative dates for lifting restrictions on different sectors.
NI's lockdown has been extended until 1 April, with a review due on 18 March.