It is up to MPs to decide whether to use their parliamentary perks to take their spouses overseas, but if they do they should realise the media will report it, Prime Minister John Key says.

He has told ministers travelling on official business to pay for their spouses themselves if they want to take them. Those trips are paid for by Ministerial Services.

The parliamentary perk of a 90 per cent air fare discount is a different rule, applying to all MPs, and is Parliamentary Services' responsibility.

Local Government Minister Rodney Hide has been criticised for using the discount to take his partner overseas, and some other ministers and beckbenchers have used it as well.

"We have a clear, open and transparent process now," Mr Key said at his post-cabinet press conference today.

"Any member who chooses to use their travel discount to take their spouse must do so in the knowledge that it will become public information, and they need to be able to stack that up with the public." He said he wasn't telling MPs not to use the discount.

"I'm saying it's up to each member to decide and consider the consequences of media intrusion if they do."

Mr Key pays for his wife Bronagh when she goes overseas with him, even when she fulfils an official role.

"I think it would be difficult for me to justify, with my independent financial means, that somehow the taxpayer should pay for me to take my family on holiday," he said.

"I don't take a fuel card, I don't take a self-drive car, I don't take lots of things."

But there were different sets of circumstances.

"You don't want 120 Members of Parliament who have the financial independence to be able to make the financial decisions that I make.

"It wouldn't be the House of Representatives, we need people from all walks of life."