Fairy Girls Vol 3

From the Kodansha edition

Erza, Lucy, Juvia and Wendy stumble upon a group of four female ruffians trying to pass themselves off as genuine Fairy Tail wizards. As they untangle the impostors' plot (with time for a few laughs along the way), the underworld of Fiore is going to learn who the real ruffians are!

Source: Anime News Network Encyclopedia