Britney Spears Lip Syncing 2014: Caught Singing Sia's Track During Piece Of Me Tour

Britney Spears was recently caught lip synching.

It is common knowledge that most musicians lip sync while performing live -- and who can blame them for taking a breather during a set of constant singing and dancing? This weekend, however, Spears was caught in the act.

On Aug. 16, a fan-based Instagram account posted a video of Spears "singing" the ballad "Perfume," but according to many fans at the show, the voice didn't belong to Spears. Instead, concertgoers believed it was the voice of Sia, who co-wrote the song.

A few months back, an acoustic version of "Perfume" was released, featuring Sia's voice on the track, and since the 38-year-old crooner has a pretty distinctive sound, it was fairly obvious to the audience that Saturday's performance of the song was not Spears.

After the video was uploaded to Instagram, a follower commented on the clip, claiming she as "second band embarrassed" for Spears. Another wrote, "Poor Britney."

This isn't the first time Spears was accused of flubbing her act during her Piece of Me residency in Las Vegas, which kicked off in Dec. 2013.

According to a June report by Radar Online, disappointed audiences have been complaining to the Planet Hollywood Resort and Casino, where the residency is held.

"The show is shockingly fake, and Britney looks bored as hell, to put it bluntly," one concertgoer complained.

Despite the plethora of accusations in regard to Spears' performance, Radar Online reported on Aug. 17 that Spears' spokesperson claimed the voice was her own. "Get your...ears checked," he said.

Spears' Piece Of Me tour is scheduled to continue at Planet Hollywood in Las Vegas until Feb. 2015.