CRA recently released a letter which considers whether a Tribal Council should be considered a public body performing a function of government within the meaning of paragraph 149(1)(c).  

CRA ruled that the Tribal Council was considered to be a public body performing a function of government in Canada within the meaning of paragraph 149(1)(c) of the Act, and, accordingly, was exempt from tax under Part I of the Act.

Here is a copy of the full CRA letter.