Jacinda Ardern says Shane Jones was wrong to wade into a case involving NZTA and a Northland trucking company.

Shane Jones, Regional Economic Development and Associate Transport Minister, has been mired in controversy after it was reported he was worried about NZTA action against the transporter.

Jones says he's concerned jobs could be on the line at Semenoff Transport, after NZTA moved to revoke its licence over safety fears.

The New Zealand First MP has since admitted he's related to the company's managing director.

The Prime Minister told Mike Hosking Jones should've stayed out of it.

"My view is that we need to act with caution when it's generally cases that could be seen as having influence attached with them.

"There is another issue which was raised a few weeks ago which was unfair on Shane. This is a case where he shouldn't have made any comments. I have talked to him about this, there are situations where comments shouldn't be made and this is one of them."

LISTEN TO THE AUDIO ABOVE AS JACINDA ARDERN SPEAKS TO MIKE HOSKING