No, it's by definition not theft. Theft is the unlawful taking of property without consent of the owner; taxation is by definition done by legal authority, and, ipso facto, is not theft.

Now, if you dismiss any moral status of legal authority (not merely legal authority which lacks some proper accountability, but all legal authority irrespective of accountability and structure), then, sure taxation is the moral equivalent of theft without being theft. And if you take the more moderate view that some legal authority is morally relevant, but that that depends on structure and accountability to the governed, then taxation by an improper authority is morally equivalent to theft.

But, by definition, taxation is not theft.