The passing of the second reading of a bill to make student union membership voluntary is an important blow in the battle to restore students' freedom of association, says Act MP Heather Roy.

Mrs Roy's Education (Freedom of Association) Amendment Bill came closer to becoming law after passing its second reading last night in the face of strong opposition from Labour and the Greens.

The legislation, which will abolish compulsory student union membership, has backing from National and United Future.

Mrs Roy said today it was an important step for freedom of choice, and that many students would be pleased with the progress of the bill.

"Students are the only sector of society compelled to join, and pay fees to, a union or organisation," she said.

"In continuing to allow this, we breach the Bill of Rights Act 1990 - which protects the rights of individuals to determine who they associate with, which political ideas they associate with, and do so without compulsion or undue influence."

She argued compulsory membership meant students couldn't study unless they paid unions fees, and were forced to pay for services many didn't use.

The New Zealand Union of Student Associations is irate about the issue and said last night it was asking for an urgent meeting with Prime Minister John Key.

"It's not too late for John Key to step in and save over a century of student representation and services from the Act Party," said co-president David Do.

"We are not asking for a law change or any government funding - all we want is for the current law, which works well, to remain."

Labour's Grant Robertson said during the first reading of the bill that it would kill off student associations and their advocacy role would be lost. "This is a straight out ideological bill," he said.

"The tertiary institutions won't provide those lost services themselves."

His colleague David Shearer said the "odious" bill would tear the heart out of the associations and would have a severely detrimental impact on campus life."

Green Party MP Gareth Hughes said it was designed to deliberately weaken student associations. "We're going to see a slashing of services across the country, like legal advice," he said.

Mrs Roy said the bill was likely to become law by early 2012.