Bruno Mars' sisters – all four of 'em-- are no joke. They are threatening to sue the all-girl 'X Factor' group known as the Lylas since the sisters already use that name!

Mars' four female sibs comprise the Lylas, an R&B singing group with a modeling contract in the Philippines. Clearly, Mars (real name: Peter Hernandez) comes from a musical family. And the good looks run in the family, as you can see from the photo of the sexy sisters above.

But they're not just pretty and talented. They also go for the jugular.

When the already existing Lylas found out about the 'X Factor' group, which were assembled from castoffs that didn't make it as solo acts and were chosen to go to the live shows by mentor Simon Cowell, they went on the offensive, attacking the group for using their name.

TMZ reports that a source close to the show claim the contestants are really shocked and upset by the accusations that they were trying to hijack the name. They didn't know another group was already using it and had domain. It sounds like it was all an honest mistake...

...and one that can be easily remedied.

The 'X Factor' edition of Lylas (pictured below) are already planning to swap out their name for a new one, and put this whole drama behind 'em.

FOX

Watch the Lylas Perform on 'X Factor'