DUP leader Jeffrey Donaldson insisted he is sending a “clear message” to the EU and the UK government about resolving issues with the Northern Ireland Protocol.
But Sinn Féin vice-president Michelle O’Neill accused the unionist party of “punishing the electorate” while Alliance Party leader Naomi Long said it had been a “shameful day” for the DUP.
The failure to elect a Speaker leaves the Stormont Assembly unable to function.
The DUP came second in the Assembly election last week in which Sinn Féin won the most seats. Under the North’s power-sharing rules, Sinn Féin would have the right to the post of First Minister, with the DUP handed the Deputy First Minister post.
A government can’t be formed unless both roles are filled, and the DUP said it won’t take part unless border checks on goods moving to Northern Ireland from the rest of the UK are scrapped.
It stymied efforts to elect a Speaker when they parties for the first time since the election yesterday.
“The DUP received a mandate to remove the Irish Sea border and our mandate will be given respect,” DUP Assembly member Paul Givan told legislators. “Our message is now clear: It is time for action, words will no longer suffice.”
Mr Donaldson said his party’s concerns over the protocol “are not merely some political squabble”. “The protocol is a direct challenge to the principles that have underpinned every agreement reached over the last 25 years of the peace process,” he said.
Ms O’Neill said the DUP was “disgracefully holding the public to ransom for their Brexit mess. Meanwhile, Many people and businesses in Northern Ireland just want a functioning government”.
“The uncomfortable truth is, while this continues, the reputational damage to Northern Ireland as a place to invest and work grows daily,” said Paul Murnaghan, president of the Northern Ireland Chamber of Commerce and Industry.
Mr Johnson’s government said the political deadlock in Belfast is proof the regulations – to which it agreed last year – are destabilising the North’s peace agreement.
The UK says it will act unilaterally to suspend some of the rules if the EU won’t agree to major changes.
British foreign secretary Liz Truss said the UK would have “no choice but to act” if the EU did not show enough “flexibility”. The UK could introduce legislation giving it the power to override the treaty as soon as next week.
The EU accuses Mr Johnson’s government of threatening to break international law by breaching a binding treaty.
Foreign Affairs Minister Simon Coveney said: “Don’t forget, this treaty was designed, ratified and agreed by the British government under this prime minister. He got a huge mandate from the British people on the back of that deal and now is blaming the deal for the problems in Northern Ireland.”