Australian lawyers are afraid petty criminals and people participating in religious festivals could be rendered stateless under citizenship changes aimed at homegrown terrorists.
Constitutional and human rights experts have also expressed grave concerns about the "irredeemable" bill.
Meanwhile, it has been revealed Fijian experts were not consulted before the Morrison government used existing powers to strip terrorist Neil Prakash of his Australian citizenship.
The government wants to make it easier to deport Australian-born extremists who are entitled to citizenship in another country.
But the Law Council of Australia fears the proposed powers would be disproportionately harsh and could breach international law.
Dual nationals sentenced to at least six years' jail for terror offences can already be stripped of their Australian citizenship.
The coalition wants to scrap the six-year threshold and expand the range of offences on which it can rely.
The Law Council's David Neal urged parliament's intelligence committee to keep the existing triggers in place.
"Low-level offending, which is dealt with to finality in a local court, could be captured by laws that lead to citizenship cessation," he told committee members in Canberra on Wednesday.
Dr Neal is also concerned the offence of "associating with a terrorist organisation" could capture people participating in legitimate social gatherings and religious festivals.
Constitutional expert George Williams believes tinkering with the bill could also capture religious pilgrims who venture into politically-sensitive areas.
"There is no actual involvement in terrorism, there is no suggestion of disloyalty, but that would trigger under this legislation the possibility of revocation," he told the committee.
Professor Williams said the bill would have a range of "extreme and unjustified" consequences and could make the community less safe.
"In fact, it may do some harm, particularly in the broader agenda of building social cohesion."
The laws would also significantly lower the threshold around proving a person's citizenship of another country.
Under the changes, the minister would only need to be "reasonably satisfied" a person may be entitled to citizenship elsewhere.
"As recent history demonstrates - in both the cases of members of parliament and the Prakash case - determining existing foreign citizenship can be difficult," Dr Neal said.
The government sparked a diplomatic fight with Fiji over the summer break after stripping Prakash of his Australian citizenship.
Home Affairs officials admitted they did not consult any experts in Fijian citizenship law before severing the terrorist's Australian ties.
Prakash was born in Melbourne to a Fijian-born father, but Fiji insists he is not and has never been a citizen.
Home Affairs officials dismissed accusations the new legislation was heavy-handed and open to legal challenge, arguing the powers were needed to protect the community, and were constitutionally sound.
