The Commission declined to comment on Monday.
The European Commission accused Ireland in 2014 of dodging international tax rules by letting Apple shelter profits worth tens of billions of dollars from tax collectors in return for maintaining jobs. Apple and Ireland rejected the accusation and have both said they will appeal any adverse ruling.
The source said the Commission will recommend a figure in back taxes that it expects to be collected but it will be up to Irish authorities to calculate exactly what is owed.
(Reporting by Padraic Halpin; editing by Ralph Boulton)