I've heard different airlines state it different ways, and even different ways on the same airline ... there's no rhyme or reason. I was surprised on a recent NW flight where they specifically allowed the use of the forward lav by coach passengers, only warning against congregating and that you would have to wait in coach.
Originally Posted by
exerda
Well, you're supposed to obey the FAs in terms of such things, and they tell you to stay in your ticketed cabin, so, though a stretch, that could be construed as the legal backing for the rule.
I was going to say the same thing, if the FA's and/or flight crew tell you to use the lav in your ticketed cabin, you would be violating FAA regulations if you disobeyed.