Two protesters from the Fireproof Australia group who blocked traffic on the Sydney Harbour Bridge have been spared jail terms.

Alan Russell Glover, 61, and Karen Fitz-Gibbon, 45, faced Sydney's Downing Centre Local Court on Tuesday after blocking traffic on the bridge for almost half an hour in April 2022.

A Hino pantech truck was parked in the left-most lane heading towards the CBD, a part of the Cahill Expressway separated from the rest of the bridge traffic by a concrete median.

Glover climbed on the roof of the truck and lit a flare, while Fitz-Gibbon glued her hand to the roadway.

"After 11 months of harsh bail conditions, the two finally have their day (or days) in court," Fireproof Australia said in a statement on Monday.

The group warned the hearings could run for up to three days as the pair "challenge the absurdity of the charges they face".

Instead, Glover and Fitz-Gibbon both entered guilty pleas to entering the Sydney Harbour Bridge and obstructing vehicles, while other charges were withdrawn on Tuesday.

Lawyers for the pair told Magistrate Daniel Reiss agreements had been reached with prosecuting police.

Both protesters had submitted they had second thoughts about the tactics used.

"Why did the penny drop so late?" Mr Reiss said.

"Why did (they) not realise beforehand, as a lot of people did?"

Glover's barrister Felicity Graham said the since-suspended Rural Fire Service member felt compelled to take more drastic action following the 2019-20 summer bushfires.

"Then there's his history of written advocacy going back decades where he's been letter writing, lobbying, doing all he can by way of advocacy within the lanes of legal political speech," Ms Graham said.

"The community will lose out if Mr Glover is convicted."

She asked for a conditional release order and no conviction recorded.

Glover and Fitz-Gibbon were both convicted and given an unsupervised community correction order, essentially a good behaviour bond, for 18 months.

They were each fined $3000.

Glover and Fitz-Gibbon sat on opposite sides of the public gallery, with legal orders preventing them communicating with one another.

As he walked out of court, Glover told reporters he was unhappy with the decision.

"The judgement is wrong and I'm going to appeal," he said.

"The RFS can take me back, I'm still a member ... the fact they've stood me down means a conviction doesn't look good for me."

The NSW government expanded the Roads Act in 2022, targeting protesters who block traffic on the Sydney Harbour Bridge and "other major bridges, tunnels and roads".

It came into effect 12 days before the action by Glover and Fitz-Gibbon, following a number of protests and public backlash, and passed parliament in less than 72 hours, supported by the Labor opposition.

The law is due to be reviewed by the end of 2024.