There are some statements by Chazal which have recently been challenged by people who claim to be Orthodox Jews. These people don't come out explicitly and declare Chazal to have been mistaken, but they do make it very clear, by their policies, that they are disputing Chazal. They seem to think that Chazal were wrong, or that the social conditions of our time have made Chazal's declarations obsolete, or that when Chazal made blanket statements they intended there to be numerous exceptions.