ACT Electoral Commissioner Damian Cantwell gave evidence at a Legislative Assembly Estimates committee on Monday, where he also raised concerns about "leakage" of such donations that could be funnelled through parties' federal branches.

While the ACT Greens and Labor promised to ban such donations during the 2016 election campaign, and a Legislative Assembly inquiry also recommended doing so, the government is yet to table legislation to enact it.

The commissioner said he was concerned about a number of "practical aspects" of the proposed ban, including the potential flow of money to ACT parties through their federal branches, and how "property developers" would be defined.

Mr Cantwell also said he had concerns about how the commission would actually monitor the ban, recommending the government create a register of "authorised" property developers in the ACT to make it easier to investigate cases.

But he said the commission did not see the policy as a "workable" one, mainly due to potential funding leaks from federal branches, and said it would also likely lead to requests from the commission for extra staff and resources to enforce it.

Mr Cantwell also said there were concerns about how to monitor donations activity, particularly if a property developer "arranged themselves in a legal sense" to get around the proposed ban.

But despite concerns an ACT ban could run afoul of the High Court's findings in NSW about the constitutionality of such bans, deputy commissioner Ro Spence told the committee it was still a "viable" proposal, if done in a measured way.

In its recent response to the Assembly inquiry into the 2016 election, the commission has also backed tightening the rules around third party campaigners in the ACT, in the wake of the CFMEU using a loophole to circumvent a cap on third party spending.

While the union used two different legal bodies to avoid directly breaching the rules, the commission also found the UFU ACT, Trades Hall Building and Clubs ACT had also overspent the $40,000 cap in the 2016 campaign, imposing fines on each of those campaigners.

The government's response to the committee in April only noted its recommendation, but the commission has backed "any recommendation aimed at tightening provisions within the Electoral Act to prevent circumventing the ACT's financial disclosure and campaign finance scheme".

The commission's response also reiterated its concern the cap on third party campaign spending should be increased, concerned it could "impermissibly burden the freedom of political communication" implied by the constitution.

But the committee did not agree with that recommendation, and the government noted its view that "the available evidence does not support a change to address the issue raised by the commission at this time".

The government has previously said it would was looking at the relevant NSW laws, as well as more recent NSW parliamentary reports on the ban on property developers, as it draws up new changes to the ACT's laws in an attempt to enact the proposed ban.

A spokesman for Chief Minister Andrew Barr has previously refused to detail what the specific definition of "property developer" would be in the ACT, amid concerns the Labor Club could be included, saying only that "will be revealed when the legislation is introduced".