NSW Labor has stood by its decision to send Tania Mihailuk to the back benches before she quit the party months out from the state election.
The Bankstown MP told parliament on Thursday she was joining the crossbench as Labor had "not cleaned up its act" and wasn't ready to govern by endorsing a candidate she believes is corrupt.
"I'm left with no other choice," she said.
Ms Mihailuk was sacked from shadow cabinet in September after using parliamentary privilege to link Labor upper house candidate and Canterbury-Bankstown mayor Khal Asfour to disgraced party powerbroker Eddie Obeid.
Opposition leader Chris Minns on Friday backed the decision to sack Ms Mihailuk, saying she'd failed to back up her claims with evidence.
"It's not unreasonable that if you're going to call somebody corrupt then you have to produce information to back up those claims and not use parliamentary privilege to do it," Mr Minns told reporters on Friday.
The Independent Commission Against Corruption had looked into Ms Mihailuk's claims and found them to be "baseless", Mr Minns said.
Canterbury-Bankstown Council also appointed independent investigator Arthur Moses SC to look into Ms Mihailuk's "unsubstantiated" allegations, he said.
Premier Dominic Perrottet pounced on Ms Mihailuk's resignation on Friday calling the state opposition "the worst division of the national Labor Party in this country".
"(Labor) are not ready to govern, it's their own side saying it," he told reporters.
"When you talk about integrity in politics, it's incredibly important that we allow people to stand up and shine the light on alleged corruption.
"That's what Tanya Mihailuk did and she has been silenced, criticised for that and sacked as a result".
But Labor MP Penny Sharpe characterised the premier's comments as hypocritical.
"It's a bit rich for the premier to talk about integrity issues when over 12 years they have lost 14 MPs as a result of ICAC investigations including two premiers," she said.
"(The coalition) have won a gold medal for pork barrelling across this state including the case where the premier's office was shredding documents so they can pork barrel into their own seats."
Ms Mihailuk told parliament she learnt Mr Minns was sacking her after a radio station producer called her. Mr Minns announced her sacking on commercial radio.
She was the subject of bullying claims in August, which she dismissed as "an internal stitch-up".
