Could this be the first serious threat to iTunes Store’s retail dominance? Seven other online music sellers have formed an alliance to promote their unique selling point - DRM-free MP3.

SEE ALSO: 7Digital Goes All-MP3, Will Pay Affiliates, Aims For US

7digital.com, Digitalstores.co.uk, HMV.com, Play.com, Tescodigital.com, Tunetribe.com and Woolworthsdownload.co.uk have been trying for months to communicate that their catalogues come without digital locks - though most folk, if stopped and asked in the street, would be unaware these stores existed. This campaign, started by the Entertainment Retailers Association’s digital wing ERA Digital, gets participating sites to wear an “MP3, 100% Compatible” badge to spread awareness.

If consumers come to understand and appreciate the fact their music can be moved between devices, the campaign may begin to one-up Apple (NSDQ: AAPL), whose store has only a relatively small DRM-free repertoire but which is still the number-one digital retail platform. ERA Digital chair and Digitalstores.co.uk CEO Russel Coultart wants it to go global: “We are in discussions with music retail organisations around the world to make ‘MP3 compatible’ an international standard.”