Forty-three groups, including the National Imams Council and Lebanese Muslim Association, have signed a letter to Attorney-General George Brandis warning that the case has not been made for the need for the so-called Foreign Fighters Bill.

The bill, which will bestow new powers on national security agencies to detain and investigate terror suspects and returning fighters, will be rushed through Parliament by the end of the month with the support of Labor.

"The government is seeking to rush this law through Parliament … doing so will deny our elected representatives and the community the opportunity to fully debate the proposed changes," the group wrote to Senator Brandis in a statement delivered on Wednesday afternoon.

"The government must explain why all of these changes are needed. Australia already has laws to meet the threat posed by foreign fighters. Indeed, the government and its agencies have formidable powers to combat terrorism. In light of this, it is not clear why some of the changes in the bill are necessary, particularly where they could have a major impact on the human rights of every Australian."

Several of the groups who signed the letters have already lodged detailed submissions to the Senate committee scrutinising the bill. It is due to report on Friday ahead of Parliament's return on Monday.

The Australian Lawyers Alliance has raised concern the new law could be unconstitutional as it will allow security agents to search houses before applying for a "delayed notification" warrant and give the Attorney-General power to suspend a terror suspect's welfare payments. In both cases, there would be no avenue to appeal to the courts.

The Muslim Legal Network, a co-signatory, raised concern in its submission that the new concept of "advocating terrorism" could preclude teachings from certain passages of texts such as the Koran and the Old Testament.

The Inspector-General of Intelligence and Security, the independent regulator overseeing the Australian Security Intelligence Organisation, has said the legislation is so wide as to redefine the meaning of "security" which could lead to any Australian who commits a criminal act overseas becoming a legitimate target of ASIO.

The organisations and individuals include constitutional expert George Williams of the University of NSW, international law Professor Ben Saul of Sydney University and Professor Hilary Charlesworth, of the Australian National University.

In its letter, the group pointed out that existing anti-terror laws do not lapse until 2015, allowing time to scrutinise new measures like the Foreign Minister's power to proscribe certain areas of conflict as "no go zones" for Australians.

"These regimes risk encroaching on rights to freedom from arbitrary detention, free speech, movement and association, without specifically addressing the threat posed by foreign fighters," the group said.

"Given the extraordinary nature of this bill, the undersigned call on the Australian Parliament to not pass the bill without a more comprehensive public consultation on the necessity of the laws and their compliance with domestic and international human rights obligations."

A spokesman for Senator Brandis declined to comment.