Canada's elections watchdog says a former Conservative cabinet minister broke election rules when he decided to wear a party-branded shirt to announce an expansion of child benefit payments.

Pierre Poilievre faced criticism in July 2015 for wearing a blue golf shirt with a Conservative logo at a government press conference promoting a bump in the value of the now defunct universal child care benefit.

The blue shirt with the large "C" on it was visible at the announcement and ensuing media availability in Halifax where Poilievre said the payments were from "our Conservative government," adding that "if the Liberals and NDP were to take office they would take the benefits away and raise taxes."

In a ruling published today, the Commissioner of Canada Elections said Poilievre's choice of leisure wear, coupled with his statements, made the occasion more like a campaign event.

The commissioner said Poilievre's words and clothing were designed to make a "positive association" between the party and the benefit to curry favourable publicity and gain a partisan advantage in the ensuing election.

In doing so, the commissioner said, Poilievre broke election financing rules. He's ordered the MP, now in opposition. to post a link to the ruling on his website, his Facebook page and his Twitter account.