Canada's language watchdog has launched an investigation into the Conservative cabinet's scrapping of the long census.

Official Languages Commissioner Graham Fraser says he wants to see whether the government respected its legal obligations when it made the decision to make the long-form census questionnaire voluntary instead of mandatory late last month.

Under the new rules, everybody will still receive a mandatory short census form, which does not ask questions about the use of Canada's official languages. One in three households will also get a long-form census survey, which has a language section, but it will not be mandatory as it currently is.

Fraser said he is worried that the loss of the detailed information provided by the long census will adversely affect francophone minority communities across Canada.

Industry Minister Tony Clement said the change was made in response to complaints about the long census voiced by Canadians, who found the long census intrusive and coercive.