Another term for it is profiteering.
It's called "price-gouging" in the States, and it
may be deemed illegal during times of an officially declared national emergency. Its illegality is declared/enacted on a state-by-state basis; i.e either the governor of a state has to issue an an executive order, or a state already has laws in place that address it in defined situations.
To my knowledge laws/orders against price gouging have always been enacted in every state during national emergencies.
Now, whether or not merchants and/or individuals pay any attention to the law is an entirely different matter.
As some wag once said about flouting laws, "It's illegal only if you get caught. "
