Unions say they're ready to take the NSW government to the High Court after Premier Gladys Berejiklian signalled sweeping changes to electoral funding laws.
Ms Berejiklian on Tuesday announced her government would introduce a suite of changes that would more than halve what third parties can spend within six months of an election.
The laws would cap electoral expenditure by third-party campaigners at $500,000. The existing limit is $1.2 million.
Unions NSW secretary Mark Morey says the planned overhaul is a bid by the coalition to silence its critics.
"It will constrain the ability of working people to get their message out - unlike the corporations who can campaign endlessly," Mr Morey told AAP, adding his organisation would go to the High Court if necessary.
"If it constrains our right to free political communication ... we will definitely challenge them. We will use whatever means necessary to make sure that we have a voice."
As well as capping third party donations, parties will have to disclose donations of more than $1000 within 14 days in the six-month period before an election.
Maximum fines for breaching donation laws will also be increased from $4400 to $22,000.
Parties will be required to identify expenditure aimed at influencing voting in specific electorates too.
"Our reforms will drive greater integrity, transparency and accountability in our electoral funding regime and help protect our democratic values and freedoms," Ms Berejiklian said in a statement.
AAP understands the government is expected to introduce the reforms to parliament on Thursday. If passed they would impact the next state election due in March 2019.
The NSW government suffered a defeat in the High Court in 2013 when it last attempted to crack down on third-party donations.
Unions NSW led the constitutional challenge which resulted in the government being ordered to pay costs of around $600,000, according to the union.