Wellington, March 16 NZPA - The job of regulating competition and fair trading in New Zealand is changing hands after business had called for drastic change.

Paula Rebstock is stepping down as chairwoman of the Commerce Commission on March 31 and lawyer Mark Berry has been appointed as chairman.

"It is with regret that I have accepted Ms Rebstock's decision to leave the commission," Minister of Commerce Simon Power said today.

He said the Government was discussing with Ms Rebstock how it might continue to use her skills and experience in other senior roles.

Dr Berry is a specialist in competition law and economic regulation and was deputy chairman of the commission between 1999 and 2001.

Ms Rebstock joined the commission in 1998 and was appointed chairwoman in 2003.

"Her leadership has been unflinching, her workload has been tremendous, and her total commitment to and belief in the benefits for business and consumers of competitive markets has been constant," said commission chief executive Nicholas Hill.

Mr Power was reported to be casting an eye over the commission after competition lawyer Grant David called for radical reform.

The media has speculated about tension between business and the commission.

Ms Rebstock led the commission when it regulated aspects of telecommunications, electricity, gas and dairy industries, affecting large corporates like Telecom, Vector and Fonterra.

The commission also said no to a plan between Qantas and Air New Zealand, prosecuted banks for poor disclosure of fees and stopped Woolworths or Foodstuffs bidding for The Warehouse.

It has also carried out prosecutions in the wood processing industry, packaging industry and air cargo industry.

Asked at his post-Cabinet press conference this afternoon if the commission had taken too much of an activist stance, Prime Minister John Key said he did not share that view.

"We back the regulator. Our view is that it is very important that we have strong competition policy in New Zealand."

The commission's role has been both applauded and criticised.

John Collinge, a former president of the National Party and former chairman of the commission, wrote in The New Zealand Herald that many of the problems of the commission today stemmed from the rushed sell-off of state assets without providing protections for competition.