If you think of first nations as small, local governments—now some not so small—they often have legal counsel involved in the drafting of their bylaws. We're in the modern age now where there are lots of advisers, lawyers and otherwise, on governance issues. If a first nation wants to engage in its law-making power, then it can assume the liability of making laws as well.
On April 23rd, 2013. See this statement in context.