Private forecasting company WeatherWatch claims MetService is engaging in ''misleading advertising'' and has taken the state-owned enterprise to the Commerce Commission.
The complaint relates to delays in passing on publicly available weather information that allows other forecasting companies to operate.
WeatherWatch managing director Philip Duncan said the difficulty in getting what was supposed to be ''open-access data'' was the ''latest frustration'' in trying to run a weather business.
In his complaint to the commission, Mr Duncan said open data meant ''data with no delays, no restrictions, no hoops to jump through''.
MetService had a website link to its ''open data'', but it was ''not open'' because other people's access to it was delayed by three to six hours, ''making this data lose most of its value and commercial use'', he said in the complaint.
''Saying they have an open-data page and then placing so many delays around access to that is misleading and clearly false advertising. How are they allowed to advertise something that isn't true?''