The government needs four crossbench votes to pass its legislation but is understood to have already secured the support of independent senator Cory Bernardi.
One Nation and Centre Alliance each control two votes.
Senator Lambie has previously said she would vote for the legislation if Construction, Forestry, Maritime, Mining and Energy Union Victorian secretary John Setka remains in his position. But she has continued to meet with unions to discuss their concerns.
Senator Lambie would not confirm her position on Tuesday.
Senator Hanson said she was sceptical about the demerit point system being considered by Mr Porter, under which union officials could be banned over repeated workplace law breaches.
“With the demerit points, what, 500, 900 [penalty units] you’re out? And a union official loses their job?” she said.
“Some of these in corporate Australia, we need to throw them out on their rear on how they do their jobs.”
Mr Porter is negotiating amendments with Centre Alliance senator Rex Patrick, who wants the bill’s public interest test for union mergers to apply only to those that repeatedly breach workplace laws.
A spokesman for Mr Porter said negotiations with Centre Alliance were ongoing.
Senator Hanson said she would not decide her position this week and could not commit to doing so by the end of the year.
Under the demerit points proposal, union officials could face an application to be disqualified from serving in a union if they or their organisation commit two or three breaches of the Fair Work Act or the Registered Organisations Commission Act.
“This is an extreme and dangerous bit of legislation [that] allows unions to be shut down and union leaders disqualified for … really minor paperwork breaches,” Australian Council of Trade Unions president Michele O’Neil said.
Senator Patrick said union officials would only be held responsible for contraventions “in their own sphere of influence” and only in circumstances where they “failed to take reasonable action to prevent the misconduct”.
Mr Porter has said the bill would not enable unions to be deregistered for minor errors.
Dana is health and industrial relations reporter for The Sydney Morning Herald and The Age.