Does the 1st amendment apply to US citizens only or anyone in the US?
constitutional law - Does the part of the First Amendment about Free Speech apply to non citizens everywhere? - Law Stack Exchange
Do non-citizens in American soil have the same rights as US citizens? Why or why not, and what are some cases where precedent was set regarding this?
Do Immigrants Have the Right to Free Speech?
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If I’m an undocumented immigrant or a foreigner visiting US, does the first amendment protect my freedom of speech too, or is it only applicable to US citizens?
Speech of foreign nationals is not treated the same as that of citizens.
In the case Buckley v. Valeo, 424 U.S. 1, the Supreme Court rules on the constitutionality of various statutory limits on campaign spending. Some parts of the law were upheld, others were overturned in 1st Amendment grounds. They upheld limits on contributions to candidates and volunteers' incidental expenses, and overturned limits on expenditures. In the decision, the court observed that
[n]either the right to associate nor the right to participate in political activities is absolute
and
"governmental 'action which may have the effect of curtailing the freedom to associate is subject to the closest scrutiny'"
The court stated that
Even a 'significant interference with protected rights of political association' may be sustained if the State demonstrates a sufficiently important interest and employs means closely drawn to avoid unnecessary abridgment of associational freedoms.
This is reasonably-standard strict scrutiny boilerplate language: what it remind you is that no Constitutionally-protected right is absolute, and all rights are subject to limitation, when that right conflicts with a compelling government interest. In the case of the federal contribution laws, that interest
is the prevention of corruption and the appearance of corruption spawned by the real or imagined coercive influence of large financial contributions on candidates' positions and on their actions if elected to office.
The court then found that
under the rigorous standard of review established by our prior decisions, the weighty interests served by restricting the size of financial contributions to political candidates are sufficient to justify the limited effect upon First Amendment freedoms caused by the $1,000 contribution ceiling.
52 USC 30121 imposes a prohibition which, if placed on US persons, would be held to violate the 1st Amendment. That law prohibits, among others,
a contribution or donation of money or other thing of value, or to make an express or implied promise to make a contribution or donation, in connection with a Federal, State, or local election
by "a foreign national", defined to not include lawful permanent residents but otherwise includes all foreign citizens and entities. The constitutionality of this law was challenged on First Amendment grounds but affirmed in Bluman v. Fed. Election Comm'n, 800 F. Supp. 2d 281 (written by Kavanaugh in his previous job), and upheld in a one-sentence affirmation by SCOTUS. So, 1st Amendment rights of foreign nationals are not protected to the same extent as those of US citizens.
It should be noted that the court also (expressly) did not decide if Congress could also constitutionally ban contributions by LPRs, or could prohibit foreign nationals from engaging in other forms of speech (issue advocacy and speaking on issues of public policy) – that matter was left undecided.
United States v. Verdugo-Urquidez, 494 US 259 (1990), holding that the Fourth Amendment does not "appl[y] to the search and seizure by United States agents of property that is owned by a nonresident alien and located in a foreign country," may have shed some light on this issue (while by no means this is conclusive on the issue of First Amendment protection over foreigners):
... While this textual exegesis is by no means conclusive, it suggests that "the people" protected by the Fourth Amendment, and by the First and Second Amendments, and to whom rights and powers are reserved in the Ninth and Tenth Amendments, refers to a class of persons who are part of a national community or who have otherwise developed sufficient connection with this country to be considered part of that community....