European law does not directly deal with the issue of local or complementary currencies but Article 178bis of the Belgian Penal Code stipulates that whosoever issues a monetary sign which is meant to circulate in public without being authorised by the competent authority, is subject to imprisonment or the payment of a fine.
This Article does not clarify which is the competent authority to authorise the issuance of a local or complementary currency, but without a doubt the National Bank of Belgium will have its say, and its opinion is in practice regularly sought by prospective issuers. Article 178bis  11 See J. VEKEMAN, “Het systeem is het probleem, niet de banken”, Trends, 11 October 2018.