Concerns raised yesterday included the level of scrutiny it had faced and the speed with which it is progressing through Parliament.
Labour peer Baroness Hayter of Kentish Town condemned the proposals, which seek to introduce a register of third-party lobbyists and put financial caps on campaigning by organisations in the run-up to general elections.
Calling it a "bad little bill", she attacked the "skeleton register" for not including in-house lobbyists.
Hayter added: "It misses most lobbyists – HS2, Heathrow, the trade associations, the ABI, the BBA, British Gas, npower and the pharmaceutical, defence, tobacco and sugar manufacturers – as they all have in-house lobbyists; and it misses most of those being lobbied."
Peers also echoed fears that the bill would restrict charities' ability to campaign, despite previous reassurances from the Leader of the House of Commons to the contrary.
The bill, which has already been voted through the House of Commons, was being debated ahead of deeper scrutiny at the Lords Committee stage scheduled for early November.