The future of the Morrison government's university fee changes is uncertain after a vote in the Senate showed a lack of majority support for the idea.
The draft legislation, which also reduces the price of "job-relevant" courses, was introduced to federal parliament last week and is being debated in the lower house.
While a Greens bid to have the bill referred to a committee for an inquiry failed in the Senate because of an even vote, if senators vote the same way for the draft laws they would fail.
Cross bench senators Jacqui Lambie, Rex Patrick and Stirling Griff sided with the Greens and Labor, leaving the committee vote tied.
Labor's education spokeswoman Tanya Plibersek says the government is hiding from scrutiny by voting against an inquiry into the bill.
"Whenever there are tough questions to answer, the Liberals run from scrutiny," she told AAP.
"If Scott Morrison thinks his plan to cut unis and jack up fees is so great, why is he trying to stop an inquiry? What has the prime minister got to hide?"
The proposed laws would more than double the cost of some humanities courses in a bid to encourage people to enrol in courses it argues lead to higher employability.
Science and maths would be among the degrees made cheaper, along with psychology, agriculture, environmental sciences and health.