"AUSA has been voluntary since 1999, and the lack of services compared to other smaller universities shows that students are being short changed," he said.
"We're asking National to be rational and drop ACT's bill. John Key can ensure that student life remains vibrant and inclusive."
Opponents of the bill have argued student unions will perish without compulsory membership because hard-up students won't pay fees, and valuable roles like advocacy will be lost.
Supporters believe student unions are the only ones in the country which still have compulsory membership, and they often don't represent the views of members.
If the bill is passed voluntary student unions will be introduced next year. New Zealand University Students Association co-president David Do said that would not give unions enough time to consult with students.
"With only eight weeks to go before students go into exams, student associations will not be able to adequately consult with their students and make preparation for a possible 100 per cent loss of income in 2012," Mr Do said.
The Lincoln union urged the Government to return to try to find a more reasonable and workable solution.
"Similar legislation in Australia had a devastating effect which the Australian government is now seeking to address, and yet our government continues to support the bill," Mrs Harper said.
"Whether it is this bill or another, the refusal to debate the issues raised eats at the very heart of democracy."
- NZPA