Eleven voluntary sector organisations have called on the government to make changes to charity campaigning rules because they represent a "fundamental threat to democracy".
In an open letter to Matt Hancock, the culture secretary, the organisations, which include Friends of the Earth, Amnesty International UK and the international development umbrella body Bond, say that in National Democracy Week it is right to point out concerns "over the lack of recognition, or engagement with, the issues civil society groups are facing".
The letter says: "We have also witnessed successive governments enacting legislation and using rhetoric that has undermined the ability of charities, and other civil society organisations, to speak out, while simultaneously reducing the public’s trust in organisations from the not-for-profit sector.
"Silencing organisations that represent the most vulnerable in society is a fundamental threat to democracy."
The letter highlights the lobbying act’s impact on charities’ ability to engage in political debate and promote local democracy, and calls for the government’s forthcoming civil society strategy, which has recently been out for consultation, to advocate a loosening of the rules.
"Your consultation asked how civil society can be supported ‘to have a stronger role in shaping government policy’," the letter says.
"Our answer is by removing the ties which constrain us when we seek to do so."
The lobbying act sets spending limits and makes it a legal necessity for all organisations that spend more that £20,000 in England or £10,000 in Wales on regulated campaigning in the year prior to an election to register with the Electoral Commission.
The act has been controversial among charities, which have made repeated calls for its repeal. An independent government review of the act carried out by the Conservative peer Lord Hodgson of Astley Abbotts proposed significant changes.
The government has already said it will not enact the reforms to the lobbying act because a lack of parliamentary time.
In its response last week to the Lords Select Committee on Citizenship and Civic Engagement’s final report, the government said third-party campaigning rules were "necessary" and ensured transparency in elections.
"The rules are not intended to prevent charities and other civil society organisations from undertaking legitimate non-party political campaigning," the government response said.
"Pressure on the parliamentary timetable means that the opportunity for legislative reform is unlikely in the near future. Instead, the government wants to work with civil society to ensure that civil society organisations have the confidence to continue their non-party political campaigning and advocacy."
Friends of the Earth was fined last year after it breached the lobbying act during the 2015 general election.