Female sports teams and leagues will now be banned from using any of Nassau County’s 100 ballfields and athletic facilities — unless they pledge to keep out transgender players.

The bombshell executive order – believed to be the first of its kind in the nation – will go into effect immediately, Nassau County Executive Bruce Blakeman announced Thursday.

“There is too much bullying going on of biological males trying to inject themselves in women and female sports and we will not tolerate that in Nassau County,” Blakeman said at a news conference.

The Republican county leader said his order only applies to female competitive sports — not co-ed sports, or sports where biological females want to compete against males.

“We are protecting girls’ right to compete against other girls,” he told The Post prior to the order coming down. “It makes no sense for biological boys who identify as transgender to compete against girls. It’s completely unfair.

“Biological boys are faster, bigger and stronger. They have a physical advantage against women.”

The county’s trans ban order was unveiled as officials engage in talks with sports leagues about licensing local facilities for the spring and summer – including a swimming center, baseball, softball and soccer fields and tennis courts, Blakeman said.

The Eisenhower Aquatic Center in East Meadow is home to the annual Big East College Swimming championship.

The action comes amid ongoing controversy over trans participation in sports, which kicked off after several transgender athletes started smashing records when they switched over to compete against biological females.

In New Jersey, trans swimmer Meghan Cortez-Field — who competed on the men’s Ramapo College team for three years — broke multiple women’s collegiate records earlier this month.

Blakeman said he decided to ban biological boys who identify as transgender girls within the past month after hearing complaints from parents and female athletes in Nassau County.

“They voiced opposition. They think it’s discrimination against girls,” he said.

Avery Graziosi, a 14-year-old freshman at Long Beach High School who attended the press conference in support, agreed.

“The competition in girls’ sports is already competitive without adding people who have more genetic capabilities. People who are stronger. Men have more physical capabilities,” the teen, who plays volleyball and softball, told The Post.

“We’re already competing at a high level, to a high standard,” she added. “The competition is intense, getting better and better each year. Why add unreasonable standards that we couldn’t possibly compete with?”

Transgender advocates, however, were quick to lash out at Nassau County’s new ban – calling it a “political stunt” by the top exec.

“It’s definitely illegal in New York,” said ­­David Klilmnick, president and founder of the Long-Island based LGBT Network.

“New York State law protects the rights of transgender individuals. Transgender women are women.”

Klilmnick added that, unlike other regions, there had been no controversy involving transgender athletes in the Long Island county.

“It’s coming out of the blue,” he said.

The New York Civil Liberties Union and state Attorney General Letitia James each said they were considering all legal options to stop Blakeman’s order.

“This executive order is transphobic and deeply dangerous. In New York, we have laws that protect our beautifully diverse communities from hate and discrimination of any and every kind,” James said in a statement. “My office is charged with enforcing and upholding those laws, and we stand up to those who violate them and trespass on the rights of marginalized communities. We are reviewing our legal options.”

Under the order, representatives from sports leagues will have to affirm in writing that trans athletes are not competing in girls’ sports to obtain the right to use the county-run or owned athletic facilities or ballfields.

“Ordered, that Nassau County Department of Parks, Recreation and Museums shall not issue any permits for the use and occupancy of Nassau County Park’s property for the purposes of organizing a sporting event or competition that allows athletic teams or sports designated for females, women, or girls to include biological males,” the order states.

It further adds that county officials may issue permits that allow teams, or sporting contests, for men or boys to include biological females – noting that “an individual’s gender is defined as the individual’s biological sex at birth.”

The edict will apply to competitive sports for all groups.