Labor is ratcheting up its lobbying of the Senate cross bench to block the Morrison government's proposed union-busting laws.
Legislation making it easier to deregister unions and ban officials is expected to be debated in the Senate this week.
The government is set to tweak the bill after negotiations with minor party Centre Alliance, which should be enough to get the laws over the line.
"This is a bill which is about destroying the right of trade unions to organise," Labor senator Penny Wong told ABC radio on Monday.
"It is about undermining the capacity of trade unions and their members to advocate for better wages and conditions and better safety."
The legislation makes it easier to deregister unions for improper conduct and repeated breaches of the law and allows for the automatic disqualification of union officials charged with serious crimes.
It also places public interest tests on union mergers.
Australian Council of Trade Unions secretary Sally McManus made a direct appeal to the crossbench senators.
"Unions will be threatened with being shut down for late paperwork. This is a sledgehammer, don't let it happen," Ms McManus said.