The federal law that prohibits dealers from requiring that a buyer not deal with a competitor is the Robinson-Patman Act. This law addresses anti-competitive practices and price discrimination, specifically in the context of maintaining fair competition among sellers. It aims to prevent unfair methods of competition and ensure that buyers have the freedom to choose among various suppliers without coercion from dealers.
A federal mandate
Local, State or Federal laws
Federal Securities Act
Federal law prohibits federal funds including Medicaid funds, from being used to pay for an elective abortion
By federal law, yes. Federal law prohibits "Undocumented immigrants."
The first amendment.
None. FEDERAL law prohibits it.
The Third Amendment prohibits the quartering of soldiers whether it be peacetime or wartime.
a mandate
Preemption
Unlikely. Federal law prohibits felons from possessing a firearm.
I believe you're looking for antitrust laws