Again, that’s a federal regulation. In this case, 27 CFR 7.21 and 27 CFR 7.27.
If the style is really a law then 90% of breweries in CA are breaking the law. Most just have the name and you can fill it with every style.
I think you are either misreading the federal law or talking about a different way of using growlers. According to the federal law you linked to, if I walk in with a growler and ask it to be filled it is considered a large glass and not subject to labeling laws.
In WA, I don’t know of very many breweries that fill growlers in advance for sale. Everyone will sell you an empty growler and fill it with the beer of your choice, or they will fill any “growler” you bring in, including mason jars or whatever, they don’t care. They can do this because there are no laws covering it in WA, and it is not a violation of federal law as explained above.
The CA law prevents them from filling growlers on the spot that have a different label, but it is not a violation of Federal law.
That isn’t how I read it, and it isn’t how our TTB rep explained it to me - but of course a different official could interpret the law differently. In our case, since I was specifically told not to fill growlers from other breweries, I won’t do it, even though there’s no Colorado law prohibiting it.
[quote]27 CFR 7.21
Malt beverages in containers shall be deemed to be misbranded:
…
(c) If the container has blown, branded, or burned therein the name or other distinguishing mark of any person engaged in business as a brewer, wholesaler, bottler, or importer, of malt beverages, or of any other person, except the person whose name is required to appear on the brand label.
[/quote]
The california law says that a brewery/brewpub can’t fill even an unbranded growler. The growler must be branded with that breweries label. The federal law as I read it states that if you are selling growlers pre-filled they must be labeled according to the labeling law for any other size bottle but if you are filling a growler upon request it doesn’t matter, it’s the same as pouring a pint in a guiness branded pint glass or a pint glass with no branding at all. and the federal labelling laws relate to the federal warnings about alcahol not specifically your name.
[/quote]
Well, you should certainly go by what your local officials and the owners tell you, since they’re the ones who will bust you if you don’t listen. 
I’m still convinced the TTB official is wrong though and you’d win in court, if you felt like going to court and all that. ;D
If you both cared and had time to deal with it, you could point out the info on the TTB’s own website for growlers filled at the point of sale (and not before). “These growlers are not subject to Federal labeling requirements.” It’s kind of hard to misinterpret that - 27 CFR 7.21 does not apply. The difference is when the growler is a “bottle” and when it is a “glass”.
From that website:
When is a growler a “large glass?”
A growler is a large glass when a consumer uses the container to make a purchase and the brewer then fills the container. Consumers may furnish their own growler or may purchase it from the brewer.
The way I’m reading it, that would depend on whether or not a “glass” is also a “container”, which may or may not be the case:
[quote]Container. Any can, bottle, barrel, keg, or other closed receptacle, irrespective of size or of the material from which made, for use for the sale of malt beverages at retail.
[/quote]
You may well be right, but I’m going to be a good boy, keep my mouth shut, and do what the government tells me. I’ll bring it up again next time I’m on the phone with TTB - which, despite the fact that they’re always very nice and very helpful, I’m hoping isn’t any time soon.
Keeping your head down sounds like a good plan If you bring it up let us know what they say. Keep my name out of it though. ;D
But really, it’s these three answers that makes me think it’s legal (federally), and you “should check with State authorities”