Words of warning to all singers: Australia does not appreciate lip-syncing one bit.

Australian critics and fans have blasted Britney Spears for lip-syncing on her Circus tour.

Now John Mayer, who is promoting his own album in Oz, is getting into the mix.

He tweeted: "If you're shocked that Britney was lip-syncing at her concert and want your money back, life may continue to be hard for you."

Find out the syncing scoop:

About 100 angry fans reportedly stormed out of Britney's Friday concert in Perth, saying they were disappointed by her performance – and lack of singing — during her show.

Spears also gave Perth fans a generic welcome, never mentioning their city's name.

"What's up, Australia?" she asked from the stage. "How you feeling tonight? It's so good to be here tonight. Your country is beautiful."

Politicians in three Australian states – Western Australia, Victoria and New South Wales – have now called for new laws to force music promoters to disclose whether a concert will be live or lip-synced.

What do you think? And hey, can we do the same thing?

Britney Spears' lip syncing was causing controversy In Australia even before she arrived for the Pacific leg of her Circus tour and now Spears is reportedly feeling the backlash.

Ticket prices are as much as $1300 for VIP seats and now that Spears has performed her first few dates Down Under, fans and critics are getting even more vicious about the quality of her show, causing Spears to become "extremely upset," according to reports.

Australia's Daily Telegraph reports that Spears holed up in her Perth hotel after fans walked out on her "lackluster" performance over the weekend (a claim her promoter, Paul Dainty, flat-out denies.)

"Britney is aware of all this and she's extremely upset about it," Dainty told The Australian. "She's a human being," he continued. "I'm embarrassed, with such a big international entourage here with Britney, to be part of the Australian media when I see that kind of totally inaccurate reporting."