The Fair Work Commission on Tuesday approved the creation of the CFMMEU, which has added "Maritime" to the name and will have around 144,000 members.
"Big business has too much power, we have record levels of inequality in our community, and working families are finding it hard to make ends meet," secretary of the new union Michael O'Connor said on Tuesday.
But the Australian Logistics Council's managing director Michael Kilgariff says the unions making up the "mega-union" have shown blatant disregard for the law.
"Allowing these two unions to combine their resources and their appetites for militancy is not in the interests of freight logistics operators, consumers or the wider community," he said.
The Australian Mines and Metals Association told the Fair Work Commission in January the new union would have revenues of almost $150 million a year, and more than $300 million in assets.
"It beggars belief that the intention of our workplace laws is to allow two unions with a history of law-breaking and many outstanding (legal) proceedings to merge," the association's Amanda Mansini said.
Workplace Minister Craig Laundy said it was not unreasonable to ask if unions who regularly break the law and aren't deterred by fines should come together.
Opposition Leader Bill Shorten said if the government was so worried about unions it should look after workers better.