The service, currently only available in the US and Canada, charges $25 (?16.22) a month and places a cap on the number of tracks a user can download.
The tracks are available as MP3, meaning the user owns them permanently and can copy/burn them an unlimited number of times.
The service is currently offering users a free trial (users must submit their credit card details first) and claims to have 8m songs in its catalogue.
A quick check shows that ZapTunes is offering music by The Beatles and AC/DC - both acts who have yet to license their sound recordings to any digital service.
Digital Music News reports that EMI is already in the process of taking legal action against the service. It quotes a ZapTunes spokesperson as saying, "Right now we are unable to provide further details about the licenses."