Energy giant AGL has pleaded guilty to 11 counts of breaking political disclosure laws after a probe prompted by anti-coal gas activists.

NSW Planning prosecuted AGL on the 11 cases, all of which the company pleaded guilty for on Friday. Sentencing is set down for a day in June.

The court outcome is a bonus for Groundswell Gloucester, a group that engaged the Environmental Defenders Office to investigate the failure of AGL to disclose in full all of donations it made to NSW Labor and Liberal parties.

The EDO's efforts focused on as much as $51,500 in reportable donations for a period after 2008, and repeated instances of failure to report donations on a timely basis.

It comes just over a week after AGL announced it would exit all CSG drilling and exploration in NSW and Queensland.

At the time of the donations, the company was seeking approval to drill as many as 110 coal seam gas wells near the mid-north coast town of Gloucester. Groundswell Gloucester made no allegation that the donations swayed the final decision to approve drilling.

"This prosecution and plea of guilty is another good example of the appalling processes involved in NSW gas and mining approvals," John Watts, a spokesman for Groundswell Gloucester, said.

"It demonstrates that even large corporations cannot be trusted to behave properly and the complete lack of proper government supervision," Mr Watts said.

Sue Higginson, principal solicitor with EDO, said it was commendable that Planning had moved to uphold "a very important law" involving development proponents making timing disclosures of political disclosure.

"But the burden is still resting with the community to identify the breaches and bring them to the regulator's attention," Ms Higginson said.

Delays in investigations also meant that developers could be seeking approvals at the same time they were making donations but the public may not be aware for some time afterwards. "A proponent can be getting away with quite a lot, which doesn't reflect well on a system with integrity, she said.

AGL said it had co-operated with Planning after launching its own investigation.

"In August 2015, we introduced a new policy prohibiting political donations to ease any community concerns," a spokesman for AGL said. "As the case is now before the Land and Environment Court, it would not be appropriate for AGL to comment any further."

Planning welcomed AGL's guilty plea.
 
A spokeswoman from the department says allegations of reportable political donation disclosure breaches are taken seriously.
"Political donation disclosures are important to ensure transparency," a spokeswoman said.

AGL is subject to a maximum penalty of $22,000 for each of these breaches. Due to legislative changes made by the NSW government in October 2014, the maximum penalty for this offence has been increased to $44,000.