The voluntary sector bodies Acevo and the Directory of Social Change have criticised the Charity Commission for having "torpedoed" an amendment that would have removed charities from the scope of the lobbying bill.
Last week, the House of Lords debated an amendment to the bill, put forward by Lord Phillips of Sudbury, to give charities an exemption from measures set out in the Transparency of Lobbying, Non-party Campaigning and Trade Union Administration Bill.
This amendment was withdrawn after an email from the commission sent to peers on Tuesday about the proposal. The commission raised concerns, including that organisations might try to set up sham charities or hijack existing charitable organisations in order to circumvent the measures in the bill.
The DSC said in a statement that the commission’s intervention had "torpedoed" the amendment.
Jay Kennedy, director of policy at the DSC, said: "We don’t agree with the Charity Commission’s arguments – in fact, we’re completely stunned by some of its points, which seem to imply that it isn’t capable of properly regulating the charity sector’s campaigning.
"The commission’s job is to apply the law, not make it. Its extraordinary intervention clearly had an impact on the debate at a key point."
Asheem Singh, director of policy at Acevo, said he was surprised at the commission’s actions. "The Charity Commission’s intervention appears increasingly ill-judged," he said. "Many in the sector will be wondering where its priorities lie.
"The commission’s letter focuses strongly on its own internal financial concerns and gives too little weight to the well-publicised concerns of the sector."
In a statement, the commission said: "We believe we had a responsibility on such a key regulatory issue to set out what we perceive to be the practical implications of the amendment, and our priority was to let peers know of our position to ensure a fully informed debate.
"If the amendment had been agreed, we believe there would have been resource implications for the commission. This point was made not as an argument against the amendment itself, but as a subsidiary point so that peers were aware of these implications. This was acknowledged in the house on Wednesday evening."
Tom Murdoch, a senior associate at the law firm Stone King, said the commission already had a difficult task in regulating think tanks and similar organisations.
"Every week the Charity Commission is criticised and, in that context, I think it’s quite reasonable to consider that anything extra it is asked to do isn’t necessarily in the best interests of public trust and confidence in charities," he said.