A Liberal backbencher has written to the federal government concerned about a crackdown on charities that critics say is designed to silence advocates.
Under the planned changes, charities risk losing their tax-deductible donation status if their resources are deemed to promote offences such as trespass or property damage.
Liberal senator Concetta Fierravanti-Wells, who chairs a committee scrutinising legislation, says the government needs to provide more information about whether the regulations are unconstitutional.
In a letter to Assistant Treasurer Michael Sukkar, Senator Fierravanti-Wells flags insufficient detail about the need for and scope of the proposed powers.
"The committee therefore requests your advice as to how the instrument is compliant with the implied freedom of political communication," the senator wrote.
"It is unclear why the specific offences are not set out on the face of the instrument, or whether there are any limitations on, or guidance in relation to, the exercise of this discretion."
Charities have expressed concerns the changes will mean they are deregistered for things like staff members blocking a footpath at a public vigil, or speaking or tweeting in support of a public demonstration.
Former World Vision head Tim Costello said the regulations are anti-democratic and will silence legitimate advocacy work.
"Giving the charity commissioner power to shutter a charity for a minor offence by a member is the equivalent of the electoral commissioner having discretion to deregister the Liberal Party because a party member damages someone's lawn when putting up a sign," he said.
"It is heartening to see that this important committee shares the concerns of charities from across the sector, which have formed a broad alliance to condemn these egregious regulations."
Mr Sukkar previously said the regulations were needed to ensure activist organisations "masquerading as charities" were no longer tolerated.
There are about 56,000 registered charities across Australia.