The Musicians Union of the UK has repeatedly accused the London Organizing Committee of the Olympic and Paralympic Games (LOCOG) of failing to compensate musicians performing at this year's Summer Olympics.

The complaints from musicians began to roll in in late June, which prompted the Musicians Union to release a statement to their members and on their website "demanding answers" to repeated examples of LOCOG staff asking musicians to play at various Olympic events for free.

"The MU has been sending LOCOG example after example of exactly that – professional musicians being asked to play Olympic gigs for which there is no budget. We have the emails to prove it – and they are coming from LOCOG staff," reads the statement posted on June 29.

Musicians Union spokesperson Isabelle Gutierrez told Billboard.biz that LOCOG originally said the compensation-free requests were coming from a "junior staff member," but the union believes this isn't the case.

"We have seen numerous emails from LOCOG targeting professional musicians saying: 'Would you like to play? We haven't got a budget for it, but it would be great exposure for you,'" Guitierrez told Billboard.biz. "Basically, we have yet to hear of one example where a professional musician is actually being paid by LOCOG. I'm sure there are some somewhere, but we are yet to find one."

UK-based musician Corey Mwamba -- who specializes in jazz and folk fusion music -- started a petition on Change.org hoping to draw further attention to the issue. The petition, which boasts 4,798 signatures as of noon on July 30, aims to draw attention to LOCOG's failure to acknowledge or compensate artists participating in the Olympics and laments the "low esteem" that LOCOG holds for artists in general.

"In short, LOCOG is not paying professional musicians for performing, citing that the publicity is adequate compensation," Mwamba wrote.

He also writes that the promised publicity is a "fiction." It's impossible to find the names of the musicians who played in the opening ceremonies on the London 2012 website, Mwamba points out, aside from the celebrity headline acts.

"All other professions involved with staging events and providing services around the Games are being contracted and paid," the petition reads. "The relationship with the arts in this case is and should be no different."

LOCOG has not responded to requests for comment.

The Los Angeles Times did point out that LOCOG had previously reached an agreement with the Musicians Union allowing certain volunteer musicians and headline artists to perform for free, but "the fine print states that 'professional' musicians are to be paid.'" There may be a fine line between a "professional" musician and a "volunteer."

Interestingly, this tiff between musicians and the Olympics comes at a time when the digital soundtrack for the opening ceremonies has hit number one on many international iTunes charts. Featuring 36 songs from the likes of David Bowie, Arctic Monkeys, U2 and Pet Shop Boys, "Isle of Wonder" is a two-disc set co-curated by Danny Boyle, who directed the show.

Other acts with music featured in the opening ceremonies have seen sales increase dramatically. Mike Oldfield, who performed his "Tubular Bells" at the ceremony, saw a 757 percent increase in sales, according to the Independent.