The government's decision to ban offshore oil exploration is heading to court after Greymouth Petroleum decided to sue the Energy Minister Megan Woods on the basis the decision is unlawful.

Greymouth Petroleum executive chairman Mark Dunphy told Mike Hosking the proper process hasn't been followed for changing the rules.

"Let's change things at the right time. Let's make sure we have got energy technologies which are affordable and efficient when we make these changes."

LISTEN ABOVE AS MARK DUNPHY SPEAKS WITH MIKE HOSKING