Simplify the following text for a Grade 12 native English-speaking person.
Original: The National Hockey League Players ' Association or NHLPA is the labor union for the group of professional hockey players who are under Standard Player Contracts to the thirty member clubs in the National Hockey League located in the United States and Canada .
Simplified: The National Hockey League Players ' Association or NHLPA is a labor union that represents the interests of the hockey players in the National Hockey League of North America .