First Minister Michelle O'Neill has said she has received a letter from police investigating protests over the Drumcree parading dispute.
On Thursday, the police said they had begun issuing letters inviting people "reasonably suspected" of committing offences linked to the protests to interview.
Unionist politicians have called for action to be taken against O'Neill and other senior Sinn Féin politicians who took part in the protests against the Orange Order march down the Garvaghy Road at the end of last month.
On Friday, Portadown deputy District Master Alastair Power said there would be "serious consequences" if the Northern Ireland Secretary intervenes to stop the march.
It is the 13th day of deadlock between residents of the mainly nationalist Garvaghy Road and the local district lodge of the Orange Order.
The Parades Commission ruled that the march could go ahead with restrictions in place.
But the parade, from Drumcree Church into Portadown, did not happen due to a large protest on the Garvaghy Road.
O'Neill has previously defended her attendance at the protest, saying she was "proud to stand with the residents" and that "when the law is wrong, I will stand firmly against it".
The police statement did not name anyone they planned to issue a letter to.
In a statement issued by Sinn Féin on Friday afternoon, O'Neill confirmed she had received a letter from the PSNI.
"I can confirm I have received a letter inviting me for a police interview in relation to a peaceful protest on the Garvaghy Road. I will co-operate with the investigation," O'Neill said.
"For the last two weeks, I have stood in solidarity with the Garvaghy Road residents as attempts were made to force an unwanted Orange march through their community," she said.
"I will continue to stand with the Garvaghy Road residents who should be allowed to live in peace and free from sectarian intimidation," she added.
Earlier, Sinn Féin President Mary Lou McDonald said the party would "cooperate" in every way it could but that they remained "comfortable" in standing up for Garvaghy Road residents.
Sinn Féin MLA Deirdre Hargey also told the BBC that she had received a letter and would seek legal advice.
Drumcree was one of Northern Ireland's most serious parading disputes, when stand-offs in the mid-to-late 1990s over attempts by the Orange Order to march along the Garvaghy Road were accompanied by riots, roadblocks and killings.
When the Orange Order was prevented by police from walking down the route in July 1995, there was a tense stand-off. It was the same for the next three years.
The Parades Commission began operating in 1998 to regulate parades and try to defuse tension around marches.
Its decision not to allow a march down the Garvaghy Road that summer has been challenged by the order for the past three decades.
Earlier this year the Parades Commission decided that the march could go ahead with restrictions in place after its original decision to stop the march was overturned in court.
Meanwhile, the Court of Appeal is considering its ruling in a legal challenge brought by the residents to block the march going ahead.
