If the non-European worker is registered as a seaman in the Belgian merchant navy pool, the type of authorisation depends on the duration of the employment in Belgium.
(art. 2.8 royal decree 09/06/1999)
You do not need to ask Brussels Economy and Employment for employment authorisation in order to work in Belgium. (automatic exemption by virtue of article 2.8 of the royal decree dated 9 June 1999)