Spanish giants Real Madrid and Atletico Madrid have been banned from registering players for the next two transfer windows.
They have been punished by world governing body Fifa for breaching rules over the transfer of minors – both clubs say they will appeal.
The ban does not cover the current January transfer window.
Atletico were fined 900,000 Swiss francs (£622,000), while Real were told to pay 360,000 (£249,000).
Real said that the claim that they had signed foreign players under the age of 18 without being properly registered was “absolutely untrue”.
“Real Madrid will appeal this decision of Fifa in all the sporting incidents, considering them absolutely inappropriate,” Real said.
Atletico said: “Our club is not in agreement with the sanction from international football’s governing body and will study all the documentation we’ve received to present an appeal against the sanction.”
Barcelona were given the same penalty in April 2014 for also breaching rules on the transfer of under-18 players.