The Nassau and Suffolk legislatures will hold a rare joint bicounty news conference Friday at the Nassau Coliseum to urge the New York Islanders to return to their former home once the arena’s Brooklyn-based developer makes unspecified “modifications” to the building.

The Nassau Legislature wrote to Islanders’ owners Jonathan Ledecky and Scott Malkin last month asking them to “give the idea of returning the team to its true home every consideration possible.” Members of the Suffolk Legislature sent a similar letter to the team and National Hockey League.

The lawmakers want Nassau Events Center, which spent $165 million to renovate the Coliseum, to increase the capacity of the 13,900-seat arena make it capable of hosting an NHL team.

“We have been assured by NEC that they are very willing to make necessary modifications to accommodate an NHL team,” the Nassau letter reads.

But in a statement to Newsday, NHL Commissioner Gary Bettman said “we do not view Nassau Coliseum as a suitable option for the Islanders.”

Sports arena experts say the Coliseum would need to add several thousand seats, dozens of luxury suites and increase the square footage and amenities of the home team’s dressing rooms to make it comparable with what’s expected of modern NHL facilities.

The Islanders, which have played at the Barclays Center in Brooklyn since 2015, declined to comment. Barclays officials are encouraging the team to opt out of its 25-year license agreement with the arena and move back to the Coliseum, according to sources familiar with the conversations.

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The two sides can opt out of the deal in January.

Brett Yormark, chief executive of Brooklyn Sports & Entertainment, the parent company of NEC, said the company is “in negotiations with the Islanders and as such cannot comment on anything specifically related to the team’s future home.”

DuWayne Gregory, presiding officer of the Suffolk Legislature, said a Coliseum return would “mean more fans spending money at local sporting goods stores, cheering their team on at restaurants and bars, hosting watch parties, and frequenting local businesses on their way to and from games.”

State officials expect to release a request for proposals soon to redevelop Belmont Park. The Islanders are expected to bid on the state-run site to build a new arena.

But in their letter Nassau lawmakers downplayed Belmont and Willets Point in Queens as homes for the team, arguing the sites “have serious neighborhood opposition” and could be the subject of local lawsuits.