The ruling means some money spent on Zed Seselja's re-election campaign will be deducted from the pool of money available to the Canberra Liberals for advertising before the October election.

The Liberal party used pictures of the ACT government's tram project on signs, direct mail-outs and advertisements during the last week of the federal election campaign to sway voters.

At least one advertisement showed ACT senator and former chief minister Katy Gallagher and Shane Rattenbury signing a power-sharing arrangement in 2012 to deliver the tram, urging voters to punish them at the polling booth.

ACT Electoral Commissioner Phillip Green said some but not all of the Liberals' federal campaign spending would be considered as material designed to sway voters in the upcoming ACT election.

"Clearly light rail is an ACT election issue and Mr Rattenbury is an ACT MLA and a member of the government, so that puts those advertisements without our purview," he said.

Mr Green said he had not informed the Liberal Party of his decision as it would not come into effect until after the election, when political parties supply a list of campaign expenses for a compliance review.

He said no laws had been broken.

"All parties have been briefed extensively on the impact of the expenditure cap and other aspects of campaign finance law and we have had some correspondence with people about what the cap applies to," he said.

Canberra Liberals' campaign manager Simeon Duncan said the party was well aware of requirements regarding campaign spending and would always comply with ACT Election Commission rulings.

But he said there was a strong argument to suggest light rail was a federal election issue given ACT Greens senate candidate Christina Hobbs promised to invest a further $400 million in the project if elected.

On January 1, the commission tightened the amount of money political parties are able to spend on messaging from $60,000-per-candidate during the 2012 election campaign, to $40,000.

The total amount major political parties can spend on campaign messaging remains $1 million, given the number of ACT parliamentarians will increase from 17 to 25 this year.

The tighter restrictions forced Unions ACT to remove its wrap-around pro-tram advertisements off the buses and to stop regular polling to avoid running into the spending cap.

Mr Green said unions would be considered as third-party campaigners with spending capped at $40,000, provided they spent more than $1000 on political advertising.

Major political parties came close to the $1 million cap during the 2012 ACT election campaign.

Labor declared $919,191 of spending with close to half amount spend on direct mail-outs, T-shirts and merchandise. Another $280,000 on television and radio advertisements, $87,000 on print ads and $75,000 on opinion polls.

The Liberals spent less at $736,669 but prioritised broadcast advertising with $480,000 on television or radio ads, $5000 on print ads, $140,000 on direct mailouts and $33,000 on opinion polls.

The ACT Greens spent $226,581 in 2012, about half on broadcast advertising.

Mr Green said the campaign spending rules were clear and enforceable, but may have been complicated by the overlap of the federal and territory election.

"When the assembly legislated for an expenditure cap they were doing so in relation to spending over a single territory election and probably didn't contemplate the overlap of a federal election," he said.

Mr Green said the commission would review the cap after the election and advise the ACT government on possible improvements.

Money spent on campaign advertising can be recouped after the October election, with political parties reimbursed $8 for each vote they secure provided they secure more than 4 per cent of the primary vote.

In 2012, the payment was just $2 although this was increased in 2014 with Liberal and Labor politicians arguing an increase in reimbursements would reduce their reliance on political donations.

Last month, electoral authorities were forced to backtrack on a warning given to ACT Liberals over their use of anti-light rail campaign material on social media.

The posts lacked an authorising statement to clarify it was from a paid member of parliament or a political party. It was later determined the posts were acceptable, provided it was clear who originally posted it.