NSW Premier Dominic Perrottett will be referred to police by a minor party that wants to know if he breached an obscure law on declarations when he joined the Liberal party, in the wake of his Nazi costume controversy.

Mr Perrottet on Sunday sought to draw a line under the controversy and again apologised for his actions, after admitting on Thursday he wore a Nazi costume to his 21st birthday party.

But NSW Shooters, Fishers and Farmers Party Leader Robert Borsak is arguing Mr Perrottet potentially broke the Oaths Act when he signed a Liberal Party preselection document around 2010 and declared he had nothing to disclose that could embarrass the party.

“It’s long past time that he be held to account, he is not above the law,” Mr Borsak said in a statement on Sunday.

It also came after Mr Perrottet said he was focused on the state, which goes to an election in March.

“I’m focused on taking our state forward … that’s what I’ve focused on my entire political life,” he said in western Sydney.

The SFF party has two upper-house members in the state parliament, including Mr Borsak and Mark Banasiak.

Mr Borsak, who is deputy chair of the parliamentary Public Accounts Committee, also said he would ask committee members to convene an urgent hearing to “examine the fitness of Mr Perrottet and his actions, to remain as Premier of NSW.”

On Sunday, Mr Perrottet, 40, was asked if any other future-Liberal politicians were at his 21st party at his parents’ home in Sydney’s northwest.

He said he couldn’t recall who was there and did not want to “drag” others into it.

“It’s not about other people, I made a mistake, it’s about what I did,” he told reporters.

“What I know was, I was there and I know what I did.”

Mr Perrottet made the Nazi costume admission on Thursday after a phone call with Transport Minister David Elliott the previous night.

On Sunday, Mr Perrottet said Mr Elliott, with whom he’d recently clashed over the issue of cashless gaming cards, didn’t have a photo of the incident and he was not aware if one existed. Mr Elliott is due to leave politics at the election.

Mr Perrottet repeated on Sunday he had made a mistake by wearing the costume, saying he was naive.

“The person I am today is not the person I was back then,” he said.

“You mature on life’s journey and that’s what (has) happened.

“As you go through life you don’t just learn from the good things, you do you learn from the mistakes you make.”

A spokesperson for the premier referred questions about Mr Borsak’s referral to the state Liberal party, saying it was a matter for the party.

Mr Perrottet maintained he has the support of his colleagues, with many publicly supporting him.

Roads Minister Natalie Ward, who was with Mr Perrottet to announce a new $1 billion Western Sydney roads package, said the premier had owned the mistake and it was not a reflection of the man she worked with.

“What I’ve seen in Dom Perrottet is a compassionate, kind person who works his guts out every day for the people of NSW,” Ms Ward said.

Labor leader Chris Minns has not called for the premier’s resignation.

“It’s not up to me to absolve him or accept his apology on behalf of the state,” he said on Saturday.

He also said doubted the admission will impact the election.

“The people of NSW will make decisions based on many other issues,” Mr Minns said.

A person found to have breached the Oaths Act could face up to five years jail.