The Democratic Unionist Party (DUP) cannot be allowed to block the Northern Ireland Assembly the Irish PM has said.
Taoiseach Micheál Martin is meeting the main Stormont parties to discuss the Northern Ireland Protocol and the assembly crisis.
The DUP is refusing to return to power-sharing unless its issues with the protocol are resolved.
It comes as the US House of Representatives Speaker Nancy Pelosi said the protocol must remain.
The assembly is not sitting after following the election on 5 May as part of its ongoing protest against the protocol.
The party took the action as part of its ongoing protest over the .
Without the election of a new Speaker, assembly members (MLAs) cannot take their seats at Stormont.
Mr Martin said it was "unheard of in the democratic world, that a parliament would not convene in the aftermath of an election".
"I have been consistent on this over the last decade, I have always been highly critical of any moves to collapse the assembly, the executive, by any party," he told theLotterryTreasure's Good Morning Ulster programme.
"I remain consistent on that part, because I am a democrat.
"We can't have a situation where one party determines that the other parties can't convene in parliament."
He added that if the executive and assembly did not return, "that would be a denial of the wishes of the people as expressed in the ballot box most recently and that's not something that should be tolerated easily".
Earlier, Mrs Pelosi said the UK government's suggestion it could act unilaterally to change the post-Brexit trading arrangements for Northern Ireland was deeply concerning and could negatively affect the Good Friday Agreement.
Responding to Mrs Pelosi, DUP leader Sir Jeffrey Donaldson said it was "absolutely evident" that the protocol was undermining the agreement.
"It has made it impossible to have power-sharing on the basis of consensus," he told Good Morning Ulster.
"If Nancy Pelosi wants to see the agreement protected then she needs to recognise that in fact it's the protocol that is harming and undermining the agreement and that's why we have to deal with it".
Ahead of his meeting with the taoiseach, Sir Jeffrey said "the unionist viewpoint can no longer be ignored".
In a statement, Sir Jeffrey added that power-sharing "only works with the consent of unionists and nationalists" and while he wanted to see Stormont's political institutions working fully, that could only happen by "building consensus".
The DUP is also refusing to nominate ministers to a new executive.
Ministers from the previous executive which collapsed in February remain in their posts in caretaker roles.
While the DUP will tell the taoiseach that its concerns over the Northern Ireland Protocol must be dealt with before the executive can be reinstated, the other parties are likely to tell him that the political blockage at Stormont is being caused by Sir Jeffrey's party.
It is the first time the DUP leader, Ulster Unionist Party (UUP) leader Doug Beattie and Social Democratic and Labour Party (SDLP) leader Colum Eastwood, will meet the taoiseach in person .
Sir Jeffrey said his party was "happy to engage with the taoiseach regarding the protocol and how our two countries operate on matters of mutual concern".
"The functioning of the Northern Ireland Assembly and executive, however, are entirely matters for the Northern Ireland parties and the UK government."
He added that the "current protocol is incompatible with the Belfast/Good Friday Agreement".
"The Irish government can't have both."
As well as talking to politicians, Mr Martin will meet business leaders.
In a tweet on Thursday evening, Sinn Féin leader Mary Lou McDonald said all eyes were on the Irish government ahead of the meetings.
"As co-guarantor of the Good Friday Agreement, Dublin must bring momentum and plans to address DUP and British obstruction of the executive," she said.
"No more drift. The people have spoken. Politics must get back to work."
'Bedrock of peace'
The Speaker of the US House of Representatives Nancy Pelosi said it was "deeply concerning that the United Kingdom now seeks to unilaterally discard the Northern Ireland Protocol".
"The Good Friday Accords are the bedrock of peace in Northern Ireland and a beacon of hope for the world," she added, in a statement.
"Ensuring there remains no physical border between the Irish Republic and Northern Ireland is absolutely necessary for upholding this landmark agreement, which has transformed Northern Ireland."
"Respectful of the will of the British people and of Brexit, I urge constructive, collaborative and good-faith negotiations to implement an agreement that upholds peace."
Good conversation with @MichealMartinTD on the Protocol.— Ursula von der Leyen (@vonderleyen) May 19, 2022
The EU and Ireland are on the same page: international agreements cannot be disapplied unilaterally.
The UK needs to work with us to find joint, workable solutions.
The @EU_Commission is playing its part. pic.twitter.com/iXfxYNUhNi
On Thursday, President of the European Commission Ursula von der Leyen said she had a "good conversation" with Mr Martin.
She said the EU and Ireland were on "the same page" when it came to the protocol and they agreed "international agreements cannot be disapplied unilaterally".
Mr Martin also held an hour-long video call with Alliance Party leader Naomi Long on Thursday.
Earlier this week he met Sinn Féin deputy leader Michelle O'Neill in Dublin, ahead of .