Simplify the following text for a Grade 7 native English-speaking person.
Original: Membership of RIANZ is open to any record label operating in New Zealand , and is dominated by the American and UK owned `` Big Four '' ( EMI , Sony , Universal and Warner Music ) who have four of the five full memberships to the RIANZ .
Simplified: Membership of RIANZ is open to any record label operating in New Zealand .