Michael Laws says he will complain to the Press Council and Broadcasting Standards Authority over media using the name Whanganui.
"I am the mayor of the Wanganui District Council and will remain so regardless of the parliamentary change," he said.
The Government decided last year that both spellings would be official, although the change has not been gazetted by Parliament yet.
"This has not stopped media - Fairfax, TV3 News and Radio New Zealand being most prominent - in wrongly naming and pronouncing our city and district's name," said Mr Laws.
His office would complain to the media bodies that using the name Whanganui was illegal and insulting to the community, he said.
"The council has chosen its spelling and like 80 percent of businesses and people...that is Wanganui without the 'h'."
In March, Mr Laws was angered by a New Zealand Transport Agency sign on State Highway 3 which referred to Whanganui. The agency removed the sign.