Lawyers have questioned the Turnbull government's reasoning behind toughening the English language requirements for aspiring Australian citizens.
The Law Council of Australia says the purpose of the move is unclear, claiming it is not substantiated by economic or social data.
President Fiona McLeod said on Thursday the introduction of a "competent" English requirement may disadvantage particular groups, such as refugees and humanitarian entrants.
She believes the threshold should be lowered, even though legislation before the Senate does not specify what the proposed level will be.
"The Law Council would argue that this definition should be provided now and not later via a legislative instrument," she said.
Ms McLeod said several of the proposed changes don't seem adequately justified, with the council suggesting a wide range of changes.
Among its concerns was giving the immigration minister the power to set aside review decisions on public interest grounds and revoke citizenship on the grounds of fraud or misrepresentation.
It is also worried about the requirement for minors to satisfy a "good character" test and the use of legislative instruments to define new eligibility criteria.
The Law Council is appearing before a Senate committee in Canberra on Thursday, as is the Department of Immigration and Border Protection.
