If the duration of the employment in Belgium is maximum 90 days (in case of successive jobs without any interruption, the previous periods are taken into account to calculate the 90 days), you need to submit the following documents:
Form
Authorisation application to employ a foreign worker for maximum 90 days - Employer in Belgium (in French or in Dutch)
Standard contract in accordance with article 12, paragraph 2 of the royal decree dated 9 June 1999 (in French or in Dutch)
The procedure requires a maximum of 90 days between the time the application is complete with Brussels Economy and Employment, and the issuance of the single permit/the notification of refusal.