Facebook Inc. was hours away from the formal announcement of its ambitious foray into financial services, but French Finance Minister Bruno Le Maire was already broadcasting his discontent.

'It's out of the question" that the social-media giant's digital money compete with sovereign currencies, Le Maire said.

That was just the first shot in a torrent of criticism and skepticism from policymakers around the world. U.S. House Financial Services Committee Chair Maxine Waters promised an aggressive response from Congress. Former European Central Bank Vice President Vitor Constancio called the initiative "unreliable and dangerous."