As noted elsewhere, Expedia and Amazon have joined in on the suit against Donald Trump, and so likely can not file an amicus brief.

Looks like Cisco did not sign either. 9 of the largest 15 IT companies in the world are US owned[1]

Looks like 5 of them did not sign up (HP, Amazon, IBM, Dell and Cisco) and 4 did (Apple, Microsoft, Alphabet and Intel)

[1] https://en.wikipedia.org/wiki/List_of_the_largest_informatio...

Amazon, as one of the plaintiffs in the case (the State of Washington is the first named plaintiff; the "et al." on the case title means there are others, which include Amazon and Expedia), can't file (alone or with others) an amicus brief, which is a brief by interested non-parties.

But it's misleading to count them as a company that choose not to sign on to the amicus brief.

You are right that they have made separate declarations of support, but are they plaintiffs? I think 'et al' refers to the sole other plaintiff, the state of Minnesota: http://stmedia.startribune.com/documents/1lori020217.pdf

You may be correct; I've seen a number of articles specifically claiming Amazon and Expedia joined the lawsuit (which has a clear and well accepted meaning), but on review there are also a lot claiming that the relation and there involvement is somewhat different, and I can't immediately find any definitive documentation of their joining as plaintiffs (they clearly weren't initial plaintiffs). Their involvement by any of the reports may still be of a kind to make it inappropriate for them to be amici, and they clearly support Washington (and Minnesota) substantively in the case, at any rate.

Yes, they do.

I suspect that Telsa, SpaceX and Palantir didn’t sign because Musk and Thiel wanted to talk to Trump in person, and possibly act as (informal) intermediaries.

Both have clearly stated they didn’t agree with most of Trump’s comments on the topic (without being crass or litigious) and can reasonably point at comments similar to yours to say that they are willing and encouraged to file a similar brief or join this one.

The first two are Elon Musk's companies and he's stated he wants to continue to try to influence Trump directly on this issue in particular: https://twitter.com/elonmusk/status/827924171661377536

Is Oracle really a surprise? Safra Catz is an immigrant herself, but she's also on the Trump advisory team and, in the end, it's still Larry's company anyway.

IBM has been sucking up to the Trump administration, presumably eyeing govt contracts. http://fortune.com/2016/12/20/trump-ibm-ginni-rometty/