Scalia added, “Words no longer have meaning if an Exchange that is not established by a State is ‘established by the State.’ It is hard to come up with a clearer way to limit tax credits to state Exchanges than to use the words ‘established by the State.’ And it is hard to come up with a reason to include the words ‘by the State’ other than the purpose of limiting credits to state Exchanges.”
Both intent and letter of the law were violated.
This is the argument that the plaintiffs put forward, and that argument was found to be wrong. As the ruling said, phrases in a law must be read within the context of the statute they are in, not in isolation, and within the context of the context of the law, the meaning is clear. Scalia has himself made this argument many times in the past, but in holding with his recent descent into blatant partisanship and hypocrisy only applies that reasoning to laws he likes.
What's even more notable is that SCOTUS used a 'plain language' reason for upholding the law, which in legal-speak basically means "the plaintiffs failed at reading".
Burn.