Mr Rees this week replaced National Assistant Secretary of the FSU, Geoff Derrick, who has taken a job as campaigns director of the Australian Council of Trade Unions.

"I have enormous regard for Anna Bligh," Mr Rees said of the former Queensland premier who is now chief executive officer of the Australian Bankers' Association, an industry group representing 25 banks across the country.

"She's chosen to line up with the banks and I've chosen to line up with the bank workers. I'm sure she gets a grin out of that as well. There'll be some things we agree on and some things we disagree on and that's just the nature of the beast."

One thing they do agree on is the banking tax. While the union was consulting its membership and working towards a policy on the federal government's proposed new $6.2 billion bank tax, Mr Rees said his personal view was that it was a "rubbish tax".

'Rubbish policy'

He said it would either be passed on to customers or impact on jobs in the sector. He supports former secretary of the federal department of Treasury Ken Henry, who is now NAB chairman in his criticism of the tax.

"My personal view, and I stress it's a personal view, is this is populist rubbish policy. The notion that you adjust the taxation rates for particular sectors is a pretty dangerous path to go down," Mr Rees said.

"My view is that it will be passed on, but if it's not passed on, then that will mean less money that banks have to look after their workers with better wages.

"If they [the government] weren't reducing the tax rates for the big end of town they wouldn't need to do this."

Mr Rees fears the levy could accelerate the offshoring of jobs which will have an impact on the quality of customer service in banks.

Mr Rees, 49, is the same age as another former NSW premier, Mike Baird, who started working for the National Australia Bank after resigning from the top job earlier this year.

"I'm sure [when] Mike and I catch up for a beer there will be mutual regard for the positions we have taken," Mr Rees said.

Tough stands

Mr Rees has been popular with both sides of politics, particularly after taking a tough stand against corruption within his own party, which ultimately cost him the premiership.

Among reasons he took the Finance Sector Union job was that it dealt with issues that were "front and centre of economic debate" in Australia.

"I think in life, particularly in political life you are defined by the causes you fight for and the issues you attach yourself to," he said.

"I have a long standing personal view that we have a right to collective action in pursuit of fair wages and good entitlements."

Facing increased automation and associated branch closures and job losses, Mr Rees said the union needed to plan for the jobs of the future and provide adequate representation for its members.

He said customers were entitled to sound advice and full disclosure when it came to buying insurance products from the banks, particularly in country towns where tellers knew many of their customers.

"We don't want our members having pressure placed on them to sell these products unnecessarily," Mr Rees said.

Union turmoil

Mr Rees has joined the FSU after a period of internal turmoil.

The FSU's former national secretary, Fiona Jordan, resigned in July last year, mid-way through a four-year term.

Her resignation followed an internal power struggle within the union's national executive where she had minority support.

The conflict culminated with Ms Jordan sending an extraordinary message to members on September 9, 2015, about a "hostile" national executive she claimed had stymied any changes she had tried to make to the union.

When FSU national secretary Julia Angrisano announced on Friday that Rees had been appointed to the national assistant secretary role she said he had "a reputation for stamping out corruption and putting the interests of honest working people first".

"Nathan brings to the FSU vast experience in delivering cultural change and making strategic choices that deliver the outcomes we're looking for in the finance industry," she said.

"Nathan has demonstrated great resilience and the ability to stand up for what is right in the face of tremendous political pressure."

Mr Rees, who has a reputation for calling a spade a spade, famously sacked former NSW ALP minister and powerbroker Joe Tripodi and former resources minister Ian McDonald from his ministry team in November 2009. The Independent Commission of Corruption later found them both corrupt.

That decision to oust them cost Rees the premiership.

Three weeks after he moved to break the hold of "malignant" forces in NSW politics, those forces (aligned with corrupt former minister Eddie Obeid) forced a leadership spill. Obeid was late last year jailed for misconduct in public office over his family's secret business dealings.