Lawyers for the main public sector union have told the industrial umpire the Immigration department has ignored workers and failed to be flexible in a bitter workplace dispute.
The Community and Public Sector Union opened its case at the Fair Work Commission in Canberra on Friday saying Immigration would not negotiate changes to its offers, and had adhered too strictly to the Coalition's public service bargaining rules.
But Immigration's legal counsel Paul O'Grady told the full bench of the commission that the union's proposed agreement could drain its cash reserves and cost $469 million more than the department's offer.
The stoush erupted over differences between Immigration bosses and staff trying to negotiate a single workplace agreement following the department's 2015 merger with the Australian Customs and Border Protection Service.
After staff overwhelmingly rejected offers from Immigration, the dispute entered Fair Work arbitration in 2016 and the matter remains unresolved as the department readies for another merger with ASIO, the Australian Federal Police and other agencies to create a Home Affairs behemoth.
Legal counsel for the CPSU, Tony Slevin, said Immigration was seeking extensive changes to workers' conditions,had failed to seek exemptions from the Coalition's bargaining policy and didn't consider the union's position in negotiations.
"This is not about robustness, this is about good faith bargaining," he said, referring to Immigration's claim that it had simply taken a strong position into talks.
"The negotiations unfolded in a manner described by witnesses that I would rely on as being 'frustrating and fruitless'," Mr Slevin said.
"The department is simply putting forward its preferred instrument and using that."
Mr Slevin said Immigration workers' 91 per cent rejection of the department's offer in September 2015 sent a strong message to their bosses, who nevertheless didn't listen.
The CPSU and departmental staff, who have gone four years without a pay rise, were not opposed to "sensible and reasonable" changes that would lead to greater productivity, he said.
Since the expiry of old agreements in 2014 their workload had increased, and was expected to grow again before 2019 as visitor arrival and visa application numbers swelled.
"Those changes do not happen because they're announced, they happen because the people on the ground accommodate them," Mr Slevin said.
Mr O'Grady earlier told the commission that the union's proposal would cost $613.9 million over three years, compared to $144.9 million for Immigration's offer.
The CPSU's proposal would bring a "day one" cost of $364 million that would sap the department's $470 million cash reserves and leave them at "dangerously low levels", he said.
The Fair Work Commission began hearings on Monday, more than a year after it halted industrial action by union members including strikes at Australia's international airports
The case continues and former senior Labor government members Wayne Swan and Craig Emerson are expected to appear later as witnesses for the union in hearings, due to finish in December.