If the non-European worker is a researcher, the type of authorisation varies based on whether or not they work in the frame of a hosting agreement and based on the duration of the employment in Belgium.
(art. 2,26 and 9,8 Royal Decree 09/06/1999)
The researcher works in Belgium in the frame of a hosting agreement (regardless the work duration)
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 2.26 of the royal decree dated 9 June 1999)
The researcher works in Belgium for more than 90 days and four years at most (without a hosting agreement) (art. 9,8 royal decree 09/06/1999)