Pandora shares are down about 11% at mid-day, a little more than a week after the company rallied from its report that sales were stronger than expected in Q1. Investors are anxious following The Wall Street Journal‘s report this morning that Apple agreed over the weekend to let Warner Music’s publishing operation collect 10% of the ad sales from a planned Internet radio service. The amount is twice as much as Pandora shares with publishers and the paper says it could “pave the way for other major publishing deals to follow.” Apple would like to unveil its Web service next week at its annual developer’s conference in San Francisco. Pandora “have traded up significantly” in recent months due in part to Apple’s slow progress in securing the rights for its rival initiative, Wedbush Securities’ Michael Pachter recently noted. Despite the progress with Warner, Apple probably won’t launch its new service unless it can also agree on terms with the publishing units of Universal Music and Sony Music, the paper says.