Constrain Rigid Body in ONE Axis direction

This may be a stupid question, but is it possible to constrain a rigid body in say "Y UP" alone ?

I know I can use FreezePositionY , but that also disables "falling". Now I can probably solve this by disabling the FreezePositionY in certain area's but that just adds more code and I prefer to do it in a single line of code over creating a bunch of if/else statements .

Thanks in advance!!!