Brussels has again warned Greece to recover 161m euros ($196m; £112m) in illegal state aid granted to Olympic Airways from 1998 to 2002.
The EU was not impressed by Olympic's slight name change
The European Commission said on Tuesday that the Greek government could face large fines if it did not comply within two months.
It follows an earlier court ruling by the European Court of Justice.
The Commission is still waiting for Olympic to return the 540m euros of state aid it has received since 2002.
Athens was found to have given Olympic an unfair advantage over its competitors through the payment of illegal state aid.
The Greek flag-carrier has been struggling for years despite receiving regular subsidies from Athens.
Two years ago, its name was changed from Olympic Airways to Olympic Airlines under a rescue plan.
The European Commission refused to accept the Greek view that Olympic Airlines was a separate entity, saying that it was a successor company to Olympic Airways.
The Greek government aims to privatise Olympic by the autumn.
It has made two previous attempts to privatise the carrier, but these failed after key bidders pulled out.