The Electoral Commission is investigating whether Deputy Prime Minister Bill English broke electoral advertising laws in a Southland school newsletter.
An advertisement for Mr English, the Southland/Clutha MP, appeared in a Gore High School newsletter on August 26 - the first day of the regulated election advertising period.
The Electoral Commission today confirmed it was looking into whether the advertisement breached electoral laws.
Along with Mr English's contact details and a National Party logo, the advertisement contained an image of a ticked box, which could make it qualify as an election advertisement.
Election advertisements must carry a promoter's statement, which Mr English's did not, and the commission has previously referred cases in which the statement was missing to the police.
A parliamentary crest on Mr English's advertisement denoted that its funding came from Parliamentary Services, which is against Parliament's rules for election advertising, and means Mr English might have to repay the money.
A spokesman for Mr English said the advertisement was printed ahead of time, and the office had been in touch with the commission to explain the situation.
"We endeavour to comply with all the rules - but in this case there appears to have been an oversight."
The cost of running the advertisement, about $30, would be included in election expenses, he said.