Real Madrid and Atletico Madrid have been banned from registering players for the next two transfer windows.
A FIFA statement said: “The two clubs were found to have violated several provisions concerning the international transfer and first registration of minor players as well as other relevant provisions with regard to the registration and participation of certain players in competitions.”
The ban does not cover the current transfer window, which runs until the end of this month.
Hence, Atletico and Real were fined 900,000 Swiss francs (£622,000) and 360,000 (£249,000) respectively.
Barcelona was handed a 14-month ban in April 2014 for a similar offence, which ended in January of this year.