The Assembly's ethics adviser, Stephen Skehill, has recommended a far-reaching register and code of ethics for people who lobby not only ministers but opposition politicians, staff and public servants.
Mr Skehill says the ACT stands out as the only jurisdiction without a register for lobbyists.
While lobbying had an important place in politics, it could lead to favouritism for certain groups, or at worst corruption, he said.
Labor and the Liberals reached a stalemate on the idea of a register, with Chief Minister Katy Gallagher wanting it to apply to all politicians and the Liberals saying it should apply only to lobbying of ministers - in line with almost every other state and territory, as well as the Commonwealth. But on Wednesday Liberal leader Jeremy Hanson said he had come round to the view it should apply to all members, in light of what had been revealed by the corruption inquiry in NSW.
"What we've seen is an example in NSW where we can see how things go wrong," Mr Hanson said. "We've reached a point now where I think that it's good to get ahead of the game. Let's err on the side of caution. There's a genuine desire in the Assembly to make sure that we remain free from any undue influence or the perception of that."
Only Queensland extends its lobbyist register beyond ministers, and even then it applies not to the whole opposition, but only to the leader and deputy leader of the opposition.
Mr Skehill said the arguments for limiting a register to ministers were weak. Ordinary members also voted on new laws, scrutinised the government and developed policies. "Where no one party has an absolute majority in the Assembly, the potential for influence by members from other parties is heightened and so too is the need for them to be able to take well-informed decisions," Mr Skehill said in advice to an Assembly inquiry.
He recommended the register be extended to lobbying of political staffers and public servants at all levels. Some regimes applied it only to senior officials, but Mr Skehill said that seemed unwise, given advice from public servants came from more junior officers as well.
Certain groups should be exempt from registering, including churches, charities, groups such as trade unions and industry associations, and members of foreign trade delegations. He also suggested an exemption for people lobbying on behalf of friends and relatives, but said that should be only for personal issues, not business or commercial affairs to avoid simply creating a loophole.
The lobbyist register would have details of the lobbyist, including former public service employment, plus everyone on whose behalf they had lobbied in the previous year.
The lobbyist code of conduct would require them to act ethically, honestly and with integrity. It also would prevent former public servants or political staffers from lobbying for a year after leaving the job on issues that they had dealt with. For Assembly members the exclusion time would be 18 months.
The proposed definition of lobbyist is someone who lobbies in the expectation of receiving a financial reward or "some other valuable consideration". NSW, Victoria and Queensland ban lobbyists from receiving success fees, but Mr Skehill said he was not convinced by the idea as it was "not immediately apparent that success fees ... are necessarily evil".
The Assembly inquiry largely accepted Mr Skehill's suggestions, but split on whether the register should apply to all members, the Labor and Greens members saying yes and the two Liberals saying no. Mr Hanson nevertheless has come to the Labor view, saying he did not change his mind but has been considering the issue.
Mr Hanson said he knew of no untoward lobbying of politicians in Canberra, but it would be "judicious to make sure that we prevent anything like that occurring in the ACT or any perception of that occurring in the ACT".
The Assembly will debate the issue in August.