The Alliance Party leader has proposed a recall of the Stormont Assembly, following days of violence and disorder in parts of Northern Ireland.
Naomi Long has called for MLAs to debate a motion condemning the recent violence and attacks on police in loyalist areas.
The party will need the signatures of 30 MLAs for the assembly to be recalled this week.
SDLP deputy leader Nichola Mallon confirmed today that the party will sign the motion.
It comes after police were attacked during another night of violence in a number of loyalist areas yesterday, leaving nine officers injured.
The PSNI said the officers were injured during disorder in Ballymena as police attempted to engage with those present at an unnotified procession in the town at Crebilly Road at around 9:35pm. The officers are expected to be able to return to duty today.
Further unrest swept across parts of Carrickfergus and Derry, with petrol bombs and other missiles thrown at officers.
In a statement, Ms Long said: “Now is the time for leadership, for the PSNI and rule of law to be supported and for every representative to show the leadership their mandate requires them to deliver.
“We are facing an extremely serious situation. Weeks of tensions from a number of issues, incited and encouraged by a number of people who really should know better, has brought us to this point.
“To the PSNI officers injured in the line of duty, to anyone who has suffered distress, loss and damage as a result of these incidents, I’m sorry the system has failed you.
“The violence has to stop, but so does the political cover given through vague comments and empty threats.
“There is no room for ambiguity – this violence must be condemned by a united Assembly, which fully supports the rule of law in Northern Ireland.
“Anything less is just allowing a culture of lawlessness to grow and further poison our community.”
Cars, a JCB digger, a phone box and bins were set alight in the Waterside area of Derry yesterday.
Police said that a brick was thrown at a taxi, which was carrying a passenger at the time, on the Limavady Road.
Officers from the PSNI Tactical Support Group (TSG) attended the loyalist Nelson Drive Estate, where a group of youths clashed with police.
The surrounding roads were blocked with fires and barricades.
It marked the seventh night police came under attack in Derry.
The disorder started when police were dealing with a security alert in the Templemore area.
The PSNI said that no police officers were injured during Monday’s spate of violence.
Derry and Strabane District Commander Darrin Jones said: “Last night, we saw further disorder in our city during which our officers came under attack again.
“Again, we saw disgraceful scenes during which cars were set on fire and property damaged.
“This is reckless and criminal behaviour, and it has to stop. It is absolutely appalling and achieves nothing except harm to our community.
“I will continue to appeal to those in our community with influence to do what they can to stop this senseless behaviour.
“I would also appeal directly to parents and guardians to know where their children are and what they are doing to ensure they do not get caught up in criminality and that they are kept safe and away from harm.
“I would appeal to everyone in the area to help defuse any local tensions and prevent any further disorder.”
Elsewhere, petrol bombs were thrown at police officers in Carrickfergus, near Belfast.
A crowd of young people gathered in the North Road area and lit a fire in the middle of the street.
Petrol bombs were sporadically thrown at police, according to witnesses.
Earlier, the PSNI had appealed to community leaders to put a stop to the disorder that has taken place throughout much of the past week.
On Monday afternoon, groups of loyalists, some wearing masks, marched through the streets in towns across the region, including Portadown, Ballymena and Markethill.
The PSNI are investigating those marches, which appear not to have been notified to the Parades Commission.
Five officers were injured after police were pelted with petrol bombs and masonry in Newtownabbey and Carrickfergus, near Belfast, on Sunday night.
The total number of police injured in incidents in Londonderry and Belfast over the Easter weekend was 32.
Petrol bombs were thrown at PSNI officers and bins and pallets set on fire in disturbing scenes in Belfast and Derry in recent days.
On Monday night, masked loyalists marched through Portadown, playing drums and flutes and waving flags.
Sinn Fein MLA John O’Dowd condemned the march, which he said was intended to intimidate the local community.
Children as young as 12 were involved in some of the incidents that took place over the weekend, police said.
Tensions have soared within the loyalist community in recent months over post-Brexit trading arrangements, which it is claimed have created barriers between Northern Ireland and the rest of the UK.
Anger ramped up further last week following a decision not to prosecute 24 Sinn Fein politicians for attending a large-scale republican funeral during Covid-19 restrictions.
All the main unionist parties have demanded the resignation of PSNI Chief Constable Simon Byrne, claiming he has lost the confidence of their community.
