As the final preparations are being made for tonight's London 2012 Olympic opening ceremony - which is expected to be watched by a global audience of close to 1 billion people - an ongoing dispute between the Olympic organizing committee LOCOG and the U.K. Musicians' Union is heating up.

The row relates to an agreement brokered between national Trade Union Congress (TUC), the Musicians' Union (MU) and the London Organizing Committee of the Olympic and Paralympic Games (LOCOG), whereby LOCOG agreed that all professional musicians performing as part of London 2012 would receive fair payment for their work. Volunteer musicians (e.g. amateur artists) and headline acts were exempt from the deal.

Despite LOCOG's commitment to paying artists performing as part of the Olympic games, the organizing body is facing a growing swell of criticism for repeatedly approaching professional musicians to perform for free.

Musicians' Union spokesperson Isabelle Gutierrez says that she has seen numerous examples of LOCOG directly contacting musicians and managers asking artists to perform for free, the first reported instance happening back in April.

Gutierrez says that on each occasion when the MU has contacted the Olympic organizing committee to complain about the issue, LOCOG has consistently denied that it has breached the terms of its agreement and instead claimed a junior staff member made an unauthorized approach to a professional musician.

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"The first example where that happened, the band in question had been approached to do fourteen gigs for no payment," she said. "When we highlighted this to LOCOG, they said: 'Very sorry. It was a mistake by a junior employee and we aren't engaging the band anymore.' That immediately sounded alarm bells, because instead of saying: 'Sorry. Yes, of course we need to pay them.' They just dropped the idea of using that band."

Gutierrez continued, "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.' 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."

Steven Haynes is one of the professional musicians approached by LOCOG to perform for free. His band Barbican Brass was contacted by a representative of the organizing committee several months ago and asked to play at the opening of an Olympic Park venue.

"We were told that it wouldn't be a paid event, but that it would be a wonderful opportunity for us to showcase our talent to the world," he said, adding that such an approach undermines musicians' profession.

"To be asked to perform for free is disrespectful of what we do for a living. It's no different from LOCOG asking the people who built the Olympic Stadium to do it for free because it's a wonderful opportunity for them to showcase their talents to the world," he states.

Following on from the controversy, U.K.-based jazz musician Corey Mwamba has set up a petition at ( campaigning for fair payment for Olympic music and arts performers. Over 4,500 people have already signed up to the petition, Mwamba said. Meanwhile, a Facebook group entitled 'Musicians Against Playing For Free At The Olympics' has attracted over 10,000 followers.

"There isn't a sensible reason why LOCOG are not paying artists to perform," Mwamba said, pointing to the £476 million of upspent London 2012 contingency funding that was saved ahead of the Games. Mwamba said that "long-term" the petition and accompanying protest "sends out a really strong warning to those organizations with a large budget that this type of sharking practice is entirely unacceptable."

"Performers absolutely deserve to get paid fairly for their services - from the recording studio to the stage," agreed Jonathan Morrish, director of PR and Corporate Communications at U.K. collection society PPL. "They contribute hugely to events and just as everyone else in the 'chain' gets a wage - catering, security, scaffolding, make-up, choreography and more - so should musicians," he adds.

LOCOG did not respond to requests to comment when contacted by