Ngo, a former Fairfield City councillor, is serving a life sentence in Long Bay jail for the 1994 assassination of Cabramatta MP John Newman.

A NSW Corrective Services Department report released last week into a jail party organised by Ngo revealed three guests were Fairfield councillors.

The councillors had visited Ngo in jail a total of 14 times, the report said.

Independent councillor Maria Heggie said the integrity of all 15 councillors had been placed in question.

In her letter to Mr Woods, Cr Heggie urged the government to suspend the council's planning powers while an immediate investigation was undertaken into Ngo and the council.

"I want the minister to call an inquiry to see if there are any established or proven links between Ngo and decisions made by the council," she said.

Cr Heggie said she had been extremely concerned after learning "some time ago" that some of her colleagues were visiting Ngo in prison.

Councillor Thang Ngo, who is no relation to Phuong, backed the calls, although he said he was confident Ngo had little influence over councillors.

"I acknowledge that the public may be concerned of any undue influence Mr Phuong Ngo may still have on Fairfield Council but in my opinion, this fear is unfounded," he said in a statement.

Labor councillor and former mayor Robert Watkins said he would support an inquiry but described the suggestions as "ridiculous".

Labor councillors are required to caucus before each council meeting "and I've never heard Ngo's name mentioned at those meetings", he told AAP.

A spokeswoman for Mr Woods confirmed the minister had received the letter and said advice had been sought from the Local Government Department.

Opposition Leader Kerry Chikarovski said revelations councillors were visiting Ngo in jail were of concern.

"There are very real concerns that Phuong Ngo, even in jail, still is exercising an influence over Fairfield Council," she told reporters.

"Those concerns need to be investigated by an independent panel."

NSW Labor Party secretary Eric Roozendaal said other claims that Ngo remained a party member were incorrect.

"He's not a member and hasn't been since 1997," he told AAP.

"His membership has been blocked on the register so he cannot reapply."