A few days after Citi Bike pulled 1,000 of its newer-model bikes out of rotation because the forks were "wearing faster than expected," the company's unionized mechanics sent a letter to management, claiming that the new Citi Bike model was weak and faulty in its entirety, and "put into question the integrity and safety of the new bikes."

While Citi Bike has attributed the need for repairs to the bikes' heavy use on NYC streets, the mechanics have countered that the fault is in the design. Their e-mail to management, first reported by the Daily News, was acquired by Gothamist on Monday.

Citi Bike's 200 full-time and seasonal mechanics, who have been unionized since summer 2015 and are represented by Transportation Workers Union Local 100, say that they first raised their concerns about the new bike to management last September.

"We tried to warn management many months ago about these safety issues with the new bikes but were completely ignored," wrote one mechanic and TWU representative in an e-mail to his coworkers last month (he asked that his name be withheld for fear of employer retaliation). "We do not want to be blamed for the catastrophic failure that is the Motivate bike."

The Citi Bike 2.0, which debuted last June, is designed by Ben Serotta, an Olympic racing bike designer. Until recently, all of his bikes were manufactured and assembled overseas, in China. The company recently opened an assembly operation in Detroit, and a Motivate spokeswoman said bikes assembled domestically have been rotated into NYC's fleet in the last few weeks.

The union alleges that the first version of Citi Bike, manufactured in Toronto, Canada by the company DeVinci, was much sturdier, and withstood three years of use with comparatively few issues. The mechanics would prefer manufacturing facilities much closer to NYC, which they say would enhance quality control.

"They [Motivate] hired Ben, whose experience is Tour de France-type bicycles, not NYC," said TWU Local 100 organizer Nick Bedell. "The China developer is very hard to communicate with. Motivate launched 1,000 of these bikes at once, and within a month problems started showing up."

In addition to fork issues, the mechanics allege that the bikes' seat tubes, which riders can adjust, are consistently "dimpling and cracking," and that the kickstand mounts are "cracking and giving way, leaving gaping holes at the bottom of the frame."

A section of the bike called the rear dropout, which cradles the back wheel inside the bike frame, allegedly becomes "skewed and uneven to the extent that they place undue stress on the rear axle and hub resulting in catastrophic axle breaks and premature hub/wheel failure."

It's worth noting that Citi Bike's functionality was far from seamless before the new bikes were introduced. The company's early software was glitchy, and Motivate was faced with a backlog of 900 busted bikes—the original design—last June.

"The new line of Citi Bikes are very popular with riders with a sleeker, more comfortable design," said a Citi Bike spokeswoman in a statement Monday. "Like with any innovation we've learned lessons and are making improvements to durability, but all Citi Bikes on the road are extremely safe—with nearly 28 million rides and no fatalities."