Northern Ireland's Deputy First Minister Michelle O'Neill has slammed the DUP as "reckless" over a threat to walk away from devolved government over the Brexit protocol.
DUP leader Jeffrey Donaldson reiterated his threat over the weekend to withdraw his party's ministers from the Stormont Executive if the UK does not take action over the protocol.
Unionists regard the post-Brexit trade arrangements as a border in the Irish Sea, and have urged the UK Government to trigger Article 16 of the accord which would suspend elements of it.
The protocol was agreed as part of the Withdrawal Agreement in order to avoid a hard border in Ireland after the UK left the EU.
DUP ministers have been boycotting meetings of the North South Ministerial Council (NSMC) as part of its opposition to the protocol.
During Executive Office questions today, Ms O'Neill accused the DUP of "playing politics".
"Threatening this institution and blocking NSMC business whilst attending the British Irish Council in Wales speaks to the DUP's hypocrisy and dysfunction," she told MLAs.
"Threatening to walk away from this institution at a time whenever our health care workers, local communities and families are looking for certainty, particularly in the midst of a global health crisis, I think, to say the approach is reckless, is an understatement."
Mr Donaldson wrote to party members reiterating his threat to collapse Stormont if the Irish Sea border is not removed..
He also criticised British Prime Minister Boris Johnson for his lack of action on the issue, which he said was "not sustainable".
Mr Donaldson also criticised Mr Johnson over alleged lockdown-breaking parties at No. 10 Downing St, saying "no-one is above the rules".
In the letter, seen by the PA news agency, Mr Donaldson said: "Last Tuesday, I met with (Brexit Minister David) Frost, the UK negotiator on the NI Protocol, and on Wednesday, I was challenging the Prime Minister in the House of Commons about the lack of movement on the Irish Sea border being removed.
"Everyone else was asking him about parties but I was determined to focus his mind on restoring NI's place in the UK.
"His answer was a standard reply with little sign of movement. That is not sustainable.
"I have given space for talks. I have been reasonable, but Brussels is being unreasonable. These talks cannot go on for years.
"The Prime Minister must realise that if there is no progress then, as I said, on 9 September our continued participation in political institutions that are being used to impose the protocol is not sustainable.
"The uncertainty is deeply damaging on so many levels."
Mr Johnson told Mr Donaldson on Wednesday that he believed the Northern Ireland Protocol could be worked "differently", but that the EU had to be convinced of this.
He did not rule out the use of Article 16 if talks with the EU do not progress.
The UK Government has repeatedly warned that it will trigger Article 16 to suspend elements of the protocol if progress is not made.
However, there is mounting concern among some unionists in Northern Ireland that Mr Johnson has yet to follow through with that threat.
"We re-entered the NI Assembly in January 2020 based on the New Decade New Approach agreement and within it a commitment from the UK government to restore NI's place in the UK internal market," Mr Donaldson added.
"It is time for the Government to fulfil that commitment."
The DUP leader also hit out at the Prime Minister over alleged breaches of lockdown rules at No. 10, telling members he buried his father at a Covid-compliant funeral.
"I buried my dad in lockdown. No one was above the rules. Anyone breaking the rules was wrong," he wrote.
"Our family had a covid compliant funeral despite us having a large extended family. It was tough when some of our family and close friends had to stay away from the funeral."
He also hit out at Sinn Fein for its "double standards", after Michelle O'Neill criticised the Prime Minister for undermining the public health message earlier this week.
"That's why I found Sinn Féin's defence of bringing hundreds onto the streets for the Bobby Storey funeral to be grossly offensive," he said.
"Without a hint of embarrassment though, Sinn Féin rushed to microphones to criticise Boris Johnson.
"Gerry Adams, Michelle O'Neill, Gerry Kelly and Mary Lou McDonald tried to play the public for fools last year.
"One rule for them another rule for the rest of us. Let us never forget Sinn Féin's ability to have double standards."
