OTTAWA - Aboriginal Affairs Minister John Duncan has resigned after improperly advocating to a tax court on behalf of a constituent.

A statement from Duncan was released late today explaining his decision to quit shortly after Prime Minister Stephen Harper announced his departure.

Duncan's cabinet duties will be taken up temporarily by Heritage Minister James Moore.

Cabinet members were asked to review their correspondence recently following revelations by The Canadian Press that Finance Minister Jim Flaherty had improperly promoted a business in his riding in its license application to the Canadian Radio-television and Telecommunications Commission.

The federal ethics commissioner reiterated that such interventions by public office holders are forbidden.

Duncan's office subsequently located his 2011 character reference on behalf of a constituent to a tax court judge, prompting his decision to resign.

Duncan, from Vancouver Island, has suffered from poor health and was seen as one of the Conservative government's less accomplished advocates during the last several months of First Nations' protests.

With the prime minister having publicly committed to a new round of negotiations over treaty issues and land-claims settlements, the leadership of the Department of Aboriginal Affairs and Northern Development is likely to take on a much higher profile in the Conservative government.