In a unanimous decision, members of the U.S. FTC (Federal Trade Comission) 
chastised Vivendi Universal and Warner Communications for restricting competition 
in the sale of "The Three Tenors" - Jose Carreras, Placido Domingo, and Luciano 
Pavarotti - audio and video products. It seems that PolyGram (a company later 
bought by Vivendi) conspired with Warner "to curb discounting and advertising to 
boost sales of recordings that the two companies jointly had distributed based on 
the tenors' concert in Paris during the 1998 soccer World Cup." 

The Register

I’m wondering whos fault the drop in sales really is. The big labels and the RIAA seem to be quite capable of making sales drop themselves.