Transform Tool in the latest Photoshop

This may be a silly question... but I'm trying to use the free transform tool to stretch an image vertically (with no scale constraints). This is a simple task (which I do all the time) but for some reason it won't let me freely stretch. It's scaling evenly horizontally and vertically (which I don't want to do on this occasion) - I'm not sure if I turned something on or if 'scaling' constraints were automatically turned on... I'm not sure.

Does anyone know how to turn off the automatic scaling on the free transform tool, so I can stretch and distort freely with the transform tool?