This is a lot of legal talk but I found this interesting.
A cardinal rule in workers' compensation is that an employee cannot sue his or her employer in civil court for a work injury except for rare circumstances involving intentional harm. But what if the employee has two employers? Does that rule apply to both employers? The answer is yes, the rule applies to both employers, so the focus in many cases is on whether there really is an employer relationship to begin with. The case of Carabello v. Jackson Dawson Communications, Inc. and Transcend Creative Group, LLC, A-3294-17T3 (App. Div. March 26, 2019) provides some helpful insight on the requirements to establish “the second employer.”

Mr. Carabello worked for the New Jersey Sports and Exposition Authority as a teamster truck driver. The NJSEA contracted with Transcend and Jackson Dawson for a Mercedes Benz event at the Izod Center which the NJSEA owned. Carabello was the only forklift operator at the Izod Center during the event. NJSEA assigned him to operate the forklift to unload the trucks of Transcend and Jackson Dawson Communications. Carabello was told to report to Jackson's head man for further instructions in securing the tent structure for Transcend and Jackson.

The head man for Jackson instructed Carabello to transport barrels filled with water using the forklift. Carabello proposed that it might be wiser to transport the barrels while they were empty but that suggestion was not followed. While loading the filled barrels on the forklift, two barrels fell off. As Carabello moved the last of sixteen barrels off the forklift, he felt a pop in his shoulder. His injury was promptly reported to the NJSEA, and the NJSEA paid workers' compensation benefits.
https://www.workerscompensation.com/...d=32734&type=7