For criminal prosecution, it is typical that most cases involving robbery are state law cases. While federal criminal laws have expanded greatly over the last few decades with ever more drug and child pornography laws, there are some cases where what seem like a routine state law robbery case can become a federal prosecution.
A case from Fargo illustrates this situation. Two men had been charged with robbing a Taco Bell restaurant, which included shooting and injuring one of the restaurant's employees. They had been charged in state court, but because the restaurant receives its supplies from Minnesota and payroll services from another state, the case was elevated to federal court under the Hobbs Act.
The Hobbs Act was created in 1948, and was designed to allow federal prosecution in the case of racketeering in labor disputes and extortion involving labor unions. The language of the statute is broader than simply labor matters and anyone who "degree obstructs, delays, or affects" commerce by robbery, extortion or threats of violence can be prosecuted for a Hobbs Act violation.
The "affects commerce" part of the statute allows a very broad application to criminal acts that go beyond labor disputes.
Federal prosecution carries significant risks for anyone accused of a crime. The U.S. Attorney's Office is supported by the Justice Department and can avail themselves of the vast resources of many federal law enforcement agencies, such as the FBI, ATF, and DEA.
In addition, sentencing under many federal laws carries mandatory minimums or potentially longer sentence terms. The Hobbs Act permits sentences up to 20 years. And federal sentences for crimes committed after 1987 do not offer parole.
Source: kfgo.com, "2 plead guilty in Fargo restaurant robbery, shooting," Associated Press, February 02, 2016