The trade body says there remain "significant areas lacking clarity" in the Lobbying Registrar scheme and while the infrastructure can be established pre-election, the "registration of activity should be deferred until after the general election".
The Government wants the registration scheme, overseen by the new lobbying registrar Alison White, to be in operation before the May election.
In its response to the consultation on the plan, the APPC highlights concerns about the impact of registration costs, saying "the cost of the register has the potential to encourage less transparency in lobbying than at present".
Iain Anderson, chairman of the APPC, said that potential registrants needed reassuring about the cost per third-party consultancy. He said "the registrar must provide more clarity on what she expects the costs for the first year of registration will be".
The APPC also said it was "concerned" by the registrar’s idea of a voluntary system encouraging registrants to disclose the identity of the minister with whom a particularly communication is made. The APPC said that this was "mission creep" and "the register should reflect what the Act says, not what the registrar – or indeed the APPC - might feel it should have said".
It adds that "if all government departments publish a timely and comprehensive declaration of ministerial meetings - a system that is already established - this is the most suitable mechanism to drive transparency in the disclosure of meetings between lobbyists and ministers".
This issue had also divided the PRCA and the CIPR, with the latter saying that the industry should agree with this request and the former having reservations.
Anderson said: "We welcome the registrar’s efforts to engage constructively with the lobbying industry. However, fully implementing the register before the election is looking like a difficult task given the ongoing lack of clarity on some fundamental issues and the need for a pilot period to ensure the industry is able to participate confidently in this new system and any glitches can be ironed out.
"That’s why today we strongly urge the registrar to focus on establishing the infrastructure necessary to operate a register and ensuring the rules governing the new system are clear to all potential registrants as an absolute priority.
"In my view this means that in all likelihood registration should commence after the general election, to avoid the new system being rushed in, with all the problems that could cause. The benefits of proceeding with caution rather than rushing through a new system would include allowing more certainty for both the registrar and potential registrants on key issues, like the number of registrants, and crucially the costs.
"Indeed, the registrar must provide more clarity on what she expects the costs for the first year of registration will be.
"The registrar’s proposal encouraging registrants to disclose the identity of the minister they communicate with is likely to create a ‘pick and mix’ approach which would not enhance transparency."