Scottish clubs have been asked to make known any payments made to players not previously declared through official contracts by the Scottish Football Association.
All 93 member clubs have been contacted after allegations surfaced surrounding crisis club Rangers.
The clubs have until Friday, April 6 to send details of any contracts made to present or former players that were not previously lodged with the SFA.
Clubs have also been warned that they could face disciplinary action if they have breached the governing body's rules.