A bike share war is brewing in New York City.

Dock-less bike share companies that offer cheap service are eying expansions in New York, forcing Citi Bike and its supporters on the defensive.

The start-ups, many of which feature a pricing model of about $1 for every 30 minutes of riding, rely on GPS-equipped bikes with rear-wheel locks that allow users to simply park their bike and lock it anywhere. Another rider, using a smartphone app, can come along and unlock the bike to start riding.

Spin, a California-based bike share company, as well as Mobike and Ofo bike shares from China, are interested in launching in New York, according to the city’s Department of Transportation. The Post reports at least two more similar companies are looking to do so as well — and as early as this summer.

Citi Bike’s supporters and transportation advocates warn that such services could result in bikes strewn everywhere — on sidewalks, in parks and outside transit hubs — with little regard for public space or the bikes themselves. They could also, of course, undermine Citi Bike. Elected officials are trying to secure taxpayer money for a Citi Bike expansion that fills existing gaps in service in the Bronx and Staten Island.

“While this model is enticing, in practice, these dock-less systems have not always yielded the promised benefits, and have placed significant burdens on sidewalks and other urban space,” said Paul Steely White, executive director at Transportation Alternatives, in a statement. “We also cannot allow other bike share operators to conduct business in a way that leads to obstructed sidewalks, public nuisance, and a damaged reputation for bike share in general.”

While neither Mobike nor Ofo responded to multiple requests for comment, Spin President Euwyn Poon, in a statement, noted that he's in favor of regulation.

“This isn't China, and we don't want foreign companies irresponsibly dumping bikes in our city,” Poon said. “We support regulation that's created in an informed and transparent manner and look forward to working with the DOT and City Hall to make that happen.”

A Citi Bike spokeswoman, in a statement, said Motivate, which operates the service, is “actively working with the city to expand to all five boroughs, bringing the same high quality of service and good union jobs to every community we operate within.”

Jessica Lappin, president of the Downtown Alliance, one of Citi Bike’s corporate partners, wrote a letter dated March 16 to Mayor Bill de Blasio asking his administration to prohibit the rollout of the bike shares, fearing “thousands of bikes dropped onto Lower Manhattan’s narrow streets without community consultation or regulation.”

Staten Island Borough President James Oddo, who has championed bringing Citi Bike to his borough, wrote a similar letter to the administration on March 24.

“We want bike share on Staten Island, but we want Citi Bike,” he wrote, “not a dangerous rip off.”

Manhattan Councilman Ydanis Rodriguez, chair of the Transportation Committee, is drafting legislation to bring further regulations to the industry.

“We take this matter very seriously and are reviewing all of our options,” said Scott Gastel, a DOT spokesman.