IORPs which also operate compulsory employment-related pension schemes which are considered to be social security schemes covered by Regulations (EC) No 883/2004 and (EC) No 987/2009 shall be covered by this Directive in respect of their non-compulsory occupational retirement provision business. In that case, the liabilities and corresponding assets shall be ring-fenced and it shall not be possible to transfer them to the compulsory pension schemes which are considered as social security schemes or vice versa.