The country’s largest transportation worker union has now expanded to Big Apple waterways.

More than 120 NYC ferry captains have joined the Transport Workers Union of America — in what the labor group hopes will put more pressure on the Big Apple for future contract negotiations.

The ferry operators, who run vessels across NYC Ferry’s routes on the East River, Hudson River and New York Harbor, voted on Friday to join the TWU.

“In the face of an aggressive and concerted anti-trade union campaign by the employer, Hornblower, NYC Ferry Captains stood strong and voted to join the Transport Workers Union,” TWU International President John Samuelsen said.

“Industrial trade unionism – organizing every job title and craft at every employer – is the pathway to worker empowerment. This is the TWU’s goal in the NYC Ferry system.”

The ferry captains are employed by Hornblower, a private company that is contracted by the New York City Economic Development Corporation to run the service.

Ferry technicians and welders voted in August to also join the union, which now reps air, bus, subway and rail line workers.