Nationals senator John "Wacka" Williams has confirmed he will cross the floor and vote against the Government to support a commission of inquiry into the banking and financial sectors.

Senator Williams has been a long-time critic of the sectors and been calling for stronger scrutiny for many years, despite resistance from the Federal Government.

The private members bill has been introduced by Greens senator Peter Whish-Wilson and supported by senators Nick Xenophon, Derryn Hinch, Jacqui Lambie and the One Nation team.

It is expected to pass the Senate easily with the support of Labor, although it will face a tougher task in the House of Representatives, even if Nationals MP George Christensen crosses the floor.

Senator Williams said opposing the bill would have made him a hypocrite.

"I have no doubt this bill will pass the Senate going on the numbers, my vote will probably make very little difference," he said.

"But as I said, I'm not going to leave this place in a bit over two years' time at some stage saying I made a hypocrite of myself.

"I'm not that sort of person."

A parliamentary commission of inquiry would have similar powers to a royal commission, which can only be called by a prime minister.

The Federal Government remains opposed to a royal commission and has instead brought banking executives before parliamentary committees for questioning.

On Wednesday, Senator Whish-Wilson told the ABC the terms of the inquiry were broad but would focus on whistleblower protections and penalties.

"We have found a way for the Parliament to do this and to take the ball away from the Prime Minister," he said.

"The parliamentary commission of inquiry is, for all intents and purposes, a royal commission.

"It reports to Parliament and part of me actually prefers that because we can control the agenda, not the executive."

Senator Whish-Wilson said the bill was "one financial scandal away" from getting enough support to pass the Lower House of Parliament.

"We think it would be important too for the banking sector to say we have nothing to hide and we are happy to have a thorough inquiry into our system," he said.