The committee's chairman, Western Australian Liberal Senator Dean Smith, said on Tuesday the committee had "determined that some of the measures outlined in the bill are likely to be incompatible with human rights".

He listed a raft of problems that the committee had identified with the bill, which was being debated in the Senate on Tuesday and which the government hopes to pass into law by Thursday night.

Senator Smith said the committee raised particular concerns about the bill's creation of a new offence for travelling to a terrorist hotspot without a good reason, and a new offence for advocating terrorism.

The latter, he told the Senate, "may result in the criminalisation of speech and expression that does not advocate the commission of a terrorist act or terrorism offence".

He conspicuously noted that the government had not explained in the bill why the new powers to police and intelligence agencies were necessary and why existing powers were not enough to tackle the current terrorism threat.

"The committee is seeking further explanation from the Attorney-General (George Brandis)," he said.

The committee is tasked with the job of assessing proposed laws' human rights implications. It also recently raised concerns about the government's proposal to make unemployed young Australians wait six months before receiving the dole.

But its objections to the foreign fighters bill are significant because five of the committee's 10 members are Coalition MPs.

He said the committee did not mean get in the way of the government's duty to protect Australians from terrorism.

Rather it wanted to "be a vehicle for more rigorous debate".