What issue prompted james otis jr. to become an outspoken critic of british colonial policies?

The issue of taxing the colonies without having proper representation in Parliament is what stirred Otis's ire. He felt that, without the colonies having in a say in their own tax scheme (because they could not vote on them), they were not being treated fairly by the Crown and Parliament.

He advocated for a separation of powers of the government and the ones enforcing the law.