Gulitti tweets Bettman saying that the Rangers were aware if the move and that he doesn't foresee any issue.
The Rangers and Islanders have an agreement that allows the Islanders to move anywhere in Nassau or Suffolk County, Queens or Brooklyn. This stems back to the Islanders paying the Rangers $4.5 million to move to Long Island in 1972 when they joined the league. The agreement was then amended in 1986 to allow the Islanders to move.
The New York Times, from June 7, 1972, says that the Islanders paid $6 million to join the league and had to pay the Rangers $5 million for territorial rights.