"Britney will be singing. As stated before, she is in vocal training -- has been for months," her representative told the New York Daily News.
But another source told the newspaper Spears won't actually be singing during her 90-minute shows at the Planet Hollywood Resort and Casino, starting Dec. 27.
"Britney does not sing. She is being paid a lot of money to lip-sync," one insider said.
"Her fans are none the wiser, but it is disingenuous of her to take their cash and not deliver a proper performance," the source said.
"She hasn't sung live for a couple of years. If the crowd thinks they are being cheated then there is likely to be an uproar, but then again look at the success of Cirque du Soleil's Michael Jackson shows. The performers in that production don't sing live, and it has been a runaway success."