New contender in race to head NSW Labor

The NSW Labor leadership race has become tighter as another contender, Steve Whan, enters the contest.

The opposition police spokesman has confirmed he is running for the position and is seeking support from his colleagues.

He joins Labor'streasury spokesman Michael Daley, who has shaped up as a favourite in the race.

Although not confirmed, Labor's upper house leader Luke Foley and acting leader Linda Burney are also expected to stand for Labor's January 5 leadership ballet.

Mr Whan says he recognises he would need to stand aside from his upper house seat and win a lower house seat to become leader.

"I also have the guts to run and win, if I can, a marginal seat," he said.

"I'm not asking for a safe seat.

"I think it's a good opportunity to have someone who has a broad perspective of the state."

Mr Whan said he offers a fresh approach to the leadership, coming from the regional electorate of Monaro in the state's south.

Responding to criticism Labor was taking too long to choose a leader, Mr Whan said a ballot was needed.

The ballot is due to be held at a caucus meeting on January 5.

NSW Treasurer Andrew Constance said it was arrogant of Mr Whan to contest the leadership.

"That's pretty arrogant and cocky given that he hasn't got a lower house seat," he told AAP.

"This has become a game of pin the tail on the donkey."

Blacktown MP John Robertson quit as opposition leader on Tuesday, a day after it was revealed he had signed a letter for Martin Place siege gunman Man Haron Monis in 2011.

Mr Robertson's resignation came three months out from the March NSW election, which Labor is widely tipped to lose.