Have you heard the one about the banks royal commission and same-sex marriage?

You could be forgiven for experiencing deja vu during the coming parliamentary week, with a pair of issues on which the Coalition and Labor are immovably opposed set to continue dominating debate.

Labor will formally decide its position on the same-sex marriage plebiscite – it’s odds-on to be against – at a meeting of opposition MPs on Tuesday.

“There’s no secret that we are deeply concerned,” Shadow Treasurer Chris Bowen told ABC TV on Sunday.

Legislation setting up the national vote is due for debate in the lower house immediately after that meeting and Labor will get a chance once again to outline the arguments against it.

This includes the nearly $200 million price tag, the impact on the mental health of young gay and lesbian Australians, and the diversion from more important referendum questions such as the recognition of indigenous people.

But the government has the numbers to get the bill through the House of Representatives and it’s listed for further debate in the Senate on Wednesday.

Bad behaviour by the nation’s biggest banks will also stay in the spotlight as Labor promises to keep up its calls for a royal commission.

It is backed by several crossbenchers, including Bob Katter who plans to introduce legislation on Monday for such an inquiry while the Greens will move to set up a parliamentary commission of inquiry with the same powers as a royal commission.

Prime Minister Malcolm Turnbull has promised to establish a tribunal to give customers legal recourse if they can’t resolve their issues with the banks.

Labor says that’s just a stunt and a diversion that won’t really help.

CEOs at the bank inquiry (clockwise) CBA’s Ian Narev, ANZ’s Shayne Elliott, NAB’s Andrew Thorburn, Westpac’s Brian Hartzer.

“There is already a banking and financial services ombudsman – what would this achieve that that doesn’t?” Mr Bowen said.

“The banks would have very substantial resources for their legal teams for this banking tribunal and the victims of banking mispractice would, almost by definition, have no resources.”

But the government says it’s Labor who knows their preferred option wouldn’t really help bank customers.

“We don’t support a banking royal commission because we think it would recklessly and irresponsibly undermine the confidence in our banking system without actually achieving anything beneficial for bank customers,” Finance Minister Mathias Cormann told Sky News.

“Labor’s pursuing a political strategy that entirely focuses on their political self-interest.”

The political self-interests of both parties will be put to one side for at least an hour this week, when Singapore’s Prime Minister Lee Hsien Loong addresses MPs on Wednesday.

-AAP