Most of the music at the London 2012 opening and closing ceremonies will be pre-recorded.
It means that big names at the showpiece global event, which have been rumoured to include Coldplay and possibly the Rolling Stones, will be singing over vocal and instrumental tracks recorded in a studio.
The Musicians' Union told The Times that the situation is "shameful", particularly coming from a nation famous for live music.
London 2012 claims it is due to the "complexities" of such a show at the Olympic Stadium in Stratford, east London.
The bowl-shaped stadium and the unreliable British weather are factors which have to be dealt with in staging the shows.
A spokesman said: "Due to the complexity involved, it's just not possible for the music in all the shows to be live.
"There will be live musical elements but many of the songs will be recorded in advance. This is standard practice for an event of this scale."
Kim Gavin, creative director of the Olympic closing ceremony, called A Symphony Of British Music, said in February: "The intention isn't to go out there and do a mime show."
Shingai Shoniwa, lead singer of the Noisettes, told last week's Evening Standard magazine that "the band is involved in the Olympics but I can't divulge any more about that".