Secretary of State Mike Pompeo said that the federal government is looking into banning Chinese social media apps like TikTok (source). Are there any current U.S. laws or regulations via which such a ban could actually be implemented?
50 USC 1702 states that
(a) In general (1) At the times and to the extent specified in section 1701 of this title, the President may, under such regulations as he may prescribe, by means of instructions, licenses, or otherwise— (A) investigate, regulate, or prohibit— (i) any transactions in foreign exchange... (B) investigate, block during the pendency of an investigation, regulate, direct and compel, nullify, void, prevent or prohibit, any acquisition, holding, withholding, use, transfer, withdrawal, transportation, importation or exportation of, or dealing in, or exercising any right, power, or privilege with respect to, or transactions involving, any property in which any foreign country or a national thereof has any interest by any person, or with respect to any property, subject to the jurisdiction of the United States
§1701 says that
(a) Any authority granted to the President by section 1702 of this title may be exercised to deal with any unusual and extraordinary threat, which has its source in whole or substantial part outside the United States, to the national security, foreign policy, or economy of the United States, if the President declares a national emergency with respect to such threat.
and §1621 enables the president to declare a national emergency.
In addition and in lieu of a declaration of national emergency, §1708 specifically addresses economic and industrial espionage cyberthreats, and (b)(1) says that
The President may, pursuant to the International Emergency Economic Powers Act (50 U.S.C. 1701 et seq.), block and prohibit all transactions in all property and interests in property of each person described in paragraph (2), if such property and interests in property are in the United States, come within the United States, or are or come within the possession or control of a United States person.
Paragraph (2) says that
A person described in this paragraph is a foreign person the President determines knowingly requests, engages in, supports, facilitates, or benefits from the significant appropriation, through economic or industrial espionage in cyberspace, of technologies or proprietary information developed by United States persons.
and b.t.w. "person" is defined as "person or entity".
It's not certain that that is the path that the ban will follow, if it happens, but it is a possible path.
They could reveal national security information. For example, the cia could create a fake account to leak information and that app could be banned.
They could be involved in drugs or illegal activity.
They could violate FCC regulations in various ways, such as obscene content, unlicensed broadcasting (extend licensing into the wifi spectrum), and disability act violations.