Infringement letters have been issued to ClubsACT, Trades Hall Building Limited and United Firefighters Union of Australia ACT branch.

Acting ACT Electoral Commissioner Ro Spence said the expenditure cap for the 2016 Legislative Assembly election was $40,000.

"ClubsACT reported electoral expenditure of $56,190.20, or $16,190.20 over the expenditure cap," Mr Spence said.

"Trades Hall Building Limited expended $41,720.78 or $1720.78 in excess of the allowable limit. The United Firefighters Union of Australia – ACT branch, overspent the cap by $697.40, reporting a total expenditure of $40,697.40."

All three organisations will have to pay twice the amount by which they overspent the cap to the territory, according to the Electoral Act 1992.

But each organisation has 14 days to demonstrate why it should not be liable to pay the penalty.

Election returns records show Trades Hall Building Limited spent nearly $30,000 on broadcast advertising during the period and $12,100 on opinion polling and research.

The United Firefighters Union spent close to the full capped amount, $39,600, on consultant and agent fees.

ClubsACT spent more than the allowable limit, $43,870, on "matters required to be authorised" and a further $12,320 on consultant and agent fees. Matters that require authorisation are any printed or electronic material that is intended or likely to affect voting.

Mr Spence said the capped expenditure period began on January 1 and concluded on polling day, October 15, 2016.

It applied to third-party campaigners, associated entities and non-party candidate groupings, as well as to party groupings who were able to spend $40,000 for each candidate contesting the election on behalf of the party.

He confirmed all three entities issued with infringement letters correctly lodged their election returns for the period in December as part of the post-election compliance review.

The election returns can be inspected on the ACT Electoral Commission's website or in person at the ACT Electoral Commission Office in Civic.