Federal frontbenchers have defended business leaders campaigning for same-sex marriage after the group came under fire from Immigration Minister Peter Dutton.

Twenty high-profile chief executives, including the heads of Qantas and the Commonwealth Bank, urged Prime Minister Malcolm Turnbull to legislate same-sex marriage earlier this week.

On Saturday Mr Dutton said the companies should "stick to their knitting" and focus on customer service, singling out Qantas boss Alan Joyce for criticism.

But on Sunday Education Minister Simon Birmingham said the group were welcome to express their views.

"Throughout history, business leaders have often stepped ahead of legislators in supporting reforms in relation to gender equity or racial equity," Senator Birmingham said.

"I see no reason as to why business leaders are not free to do likewise when it comes to issues like marriage equality."

Foreign Minister Julie Bishop also said Australia was a democracy and free speech should be protected.

"People are free to take part in public debates and this is an issue that I'm sure will be the subject of public debate for some time," she said.

"If chief executives believe that it's in the interests of their company to collaborate on a public statement, then they're free to do so."

Their comments came as Coalition MPs hosed down newspaper reports that moderate Liberals planned to put the issue back on the agenda this week.

Deputy Prime Minister Barnaby Joyce said no-one had approached him about reigniting debate and the matter had already received enough attention last year.

"We have so many issues we need to talk about," Mr Joyce said.

"We've got to make sure we get energy security right, we've got to make sure we keep the lights on, we've got to make sure we keep the returns going we're getting for agricultural product, we've got to make sure we get the childcare issues fixed up.

"We've got so many issues we need to occupy the time of government with."

Senator Birmingham said the Government would not be distracted from those priorities in the lead-up to the May budget.

"Of course people are free to put their propositions to the Prime Minister, to the Cabinet, to the party room," he said.

"That's the freedom of a democracy and we can work through those issues.

"But it won't distract us from our focus in relation to passing childcare reforms or the like."