The Evangelical Alliance is calling upon the Government to abandon proposals to regulate homeschooling across England.
The Government is consulting on plans to introduce a local authority registration system for children who do not attend state-funded or registered independent schools.
Launching the consultation in April, Education Secretary Damian Hinds said that the aim was not to clamp down on parents doing an "admirable job" of homeschooling their children but rather to stop vulnerable young people from "vanishing under the radar".
Under the proposals, local authorities would be able to intervene where they suspected that a child was not receiving any education at home or where the education being provided was either not up to standard or only of a religious nature.
In such cases, the council would be able to force parents to enroll their children in a mainstream school.
The Evangelical Alliance said the proposals were "marred by ambiguity" and "could potentially lead to the state regulation of church life".
In addition to concerns around homeschooling, it questioned plans to impose a legal obligation upon "proprietors" of "settings" to maintain registers of attendance for state inspection upon request.
While the plans propose sanctions for those who fail to keep such registers, the Evangelical Alliance criticised the lack of clarity in the consultation as to what constitutes a "setting" or "proprietor".
It fears that the ambiguity will open the door to future regulation of a whole raft of activities provided by churches and other civil society groups, and the creation of a national registration system "entangling much of wider civil society including museums, sports clubs, even some grandparents caring for their grandchildren".
Simon McCrossan, head of public policy at the Evangelical Alliance, said the proposals were "far-reaching" and "bureaucratic".
"Civil society and the state are different things, and time and again we see that registration leads to regulation which in turn leads to the limiting of religious freedom," he said.
"The ambiguity and the refusal of the Government to clarify the purpose and scope of these regulations leads to a grave concern that there will be a chilling effect on the church's ability to practice and proclaim its faith in Jesus.
"In their current form, these plans hold open the door to a state register of attendance at church activities and will impact both religious and non-religious groups alike – from bell ringers to youth clubs – because there is no clarity as to their scope and the ambiguity seems intentional."
The latest consultation has been launched not long after the Government abandoned different proposals to regulate out-of-school settings only last year. The Evangelical Alliance warned at the time that the proposed registration could lead to the regulation of Sunday schools and other church activities.
The Evangelical Alliance said the new proposals on the table were even more wideranging and would lead to an "unprecedented intrusion upon religious activity".
Mr McCrossan went on to say: "It looks like these proposals could lead to the registration of early morning prayer meetings and after-school bible studies.
"This would be an unacceptable and unprecedented infringement of religious liberty more readily associated with regimes that have dubious human rights records.
"Although the government responded to our legitimate request for clarification, the ambiguous nature of their response suggests that these proposals do pose a threat to church life and wider civil society activity and must not go forward."
The Evangelical Alliance is encouraging people to respond to the consultation and has published a guide to offering pointers.