The National Coalition for Independent Action has called on charities and voluntary groups to consider breaking the law by defying the requirements of the lobbying act.
The group, which campaigns for the independence of the voluntary sector, said the legislation, which it calls the "gagging act", will restrict charities’ expenditure on campaigning and limit their ability to speak up for the people they exist to serve.
Charities and voluntary groups campaigned against the Transparency of Lobbying, Non-party Campaigning and Trade Union Administration Act 2014, which gained royal assent last month, because of concerns the legislation would significantly impair their ability to speak out on issues that could be regarded as party political in the run-up to elections.
Andy Benson, co-director of the NCIA, said those opposed to the act should follow through on their concerns and "defy these unjust limits on free expression".
"Civil disobedience should not be done lightly, but it is sometimes a fair response to an unfair law," he said. "We are asking charities and other groups to say they will be willing to break the gagging act if this is needed to serve the people for whom their organisations exist."
Benson said the new law was framed in such a complex way that many charities would censor themselves for fear of falling foul of the restrictions, ending up in a "spider’s web of compliance".
He said the NCIA was asking charities and campaigning groups to come together and commit acts of civil disobedience when the new law comes into effect.
Benson said it was too early to say in what specific way organisations would break the law and what acts they could commit.
"There are a number of opportunities and those would depend partly on which sort of charities take part," he said. "There are possibilities around registration, spending limits and thresholds.
"What we are saying at this stage is don’t accept that this law is a just law. People should not commit their energies to how they might comply; we should direct our attention to how we can make it unworkable."
The legislation will introduce spending limits on campaigns that "could be reasonably regarded as intended" to favour particular parties or candidates to £319,800 in England, £55,400 in Scotland, and £30,800 in Northern Ireland.
The bill became law without amendments introduced in the House of Lords on constituency spending limits, which are £9,750 per constituency, and some staff costs.
A spokeswoman for the Electoral Commission, which is due to publish its guidance on the act by early July, said the government would bring forward a statutory instrument that would set out the sanctions available to the regulator under the act.
"Once the statutory instrument has been brought forward, we will be able to advise charities more closely," she said. "We will be able to use a range of sanctions, as we do with political parties at the moment. We will have to use them against organisations if they do not comply with the legislation."