Trade Minister Tim Groser has been warned, after a complaint was made about rowdy drinking and disruptive behaviour by him and some members of a trade mission on a flight from Dubai in April.

But another member of the delegation has defended the minister, saying that if he had a few drinks they were "well deserved" after a stressful trip.

A complaint about the behaviour of the delegation and the minister on the April 30 flight was made to the Prime Minister's office.

Chief of staff Wayne Eagleson spoke to Mr Groser on behalf of Prime Minister John Key, a spokesman for Mr Key said last night.

"The minister acknowledged there had been some drinking on the flight, but he felt his behaviour was appropriate," he said.

"The Prime Minister made it quite clear through his chief of staff the expectations he had in terms of ministers' behaviour."

Mr Key was to have led the trade mission, but he decided to return to New Zealand early for the funeral of three airmen killed in an Air Force helicopter crash at Paekakariki.

Mr Groser led it instead and in the middle of it, on April 27, his mother died.

One delegate on the mission, who was not on the same flight, defended Mr Groser.

"He did a splendid job under trying circumstances," said lobbyist Matthew Hooton. "Officials let him down with poor logistical planning. They even lost his luggage and his passport on the same day he lost his mother.

"At the same time, he had to step up and stand in for the Prime Minister, and if he had a few drinks on the way home, they were well deserved."