"So we think the activists' attention to us is misplaced," she said. "If they want to change government policy, they should engage directly with the government."

The company has run the federal government's refugee detention facilities on Nauru and Manus Island since 2012, under a contract estimated to be worth $2.7 billion

More controversy

Now its tax affairs appear set to create more controversy.

Senator Dastyari said on Sunday "Transfield has had effective tax rates of between 2 per cent and 15 per cent over the past 10 years, depending on which method you use".

Senator Sam Dastyari says Transfield Services has had effective tax rates of between 2 per cent and 15 per cent over the past 10 years, depending on which method is used. Daniel Munoz

"The subsidiary structure that has been created by Transfield resembles those used by some of the most aggressive tax minimisers," he said.

"We should have concerns that, in Transfield, we are not awarding contracts to a company that structured itself to minimise its tax obligations."


Senator Dastyari noted that recommendations of the interim report of the Senate inquiry included that there should be mandatory notification "by agencies to the relevant portfolio minister when contracts with a dollar value above an agreed threshold are awarded to companies domiciled offshore for tax purposes".

"We think that you should be encouraging best behaviour," he said.

Protesters at a rally outside Transfield Services' head office organised by a group of unions concerned about human rights violations in detention centres. Eddie Jim

Immigration Minister Peter Dutton, whose department awarded Transfield a contract in September 2012 to provide services on Nauru and is in the process of extending the contract for another five years, said activists should not be punishing the company for carrying out work.

Policy won't change

"If the activists have a gripe about a political issue, they need to prosecute that in the political arena, not in the business area," he said. "The policy is supported by both the government and by Labor. If Bill Shorten wins the next election, this policy won't change."

Mr Dutton also called on superannuation funds, some of whom have sold out of Transfield's stock after coming under pressure from members concerned about alleged human rights abuses at the centres, to stand up to activists.

"The responsibility really is with major investors and the super funds and fund mangers to make clear this sort of political activism has no place in the Australian marketplace," he said.

"That would send the clear message this political witch-hunt won't succeed, won't achieve the desired outcome and that they won't divest from a lobby group involved in lawful activity."

Comment was being sought from Transfield Services.