Boycotting or "voting with your pocketbook" is a form of free speech. You can in general support (or not support) anything you want that isn't a crime, but other people can support—or not support—what they want too.
There are prohibitions against government making distinctions based on speech/ political position (although occasionally political position will coincide with experience/ non experience relevant to that position: for example interacting with a variety of people tends to make one more liberal, so things like traveling to learn about cultures, moving from one town to another, living in a diverse city, or attending university, would make one more liberal because once they understand that people are different yet similar, they have little interest in preserving a status quo that keeps people contained in arbitrary boxes while denying the basic needs or full humanity of some people).
However there are, for good reasons, no prohibitions on individual people living individual lives, making choices what to support based on our own values.
FTC is out of line investigating boycotts. They need to be strongly reminded of their actual mission to support fairness towards consumers. Like any federal agency, their job is not to promote the political priorities of the current president, whomever that may be. Their job is to support our Constitution and our laws in a particular sphere.
best wishes