Mobile phone services were disabled in four New tunnels immediately after the London bombings, officials say.
Extra security was put in place in New York after the London bombs
Transmitters were switched off in Manhattan's Holland, Lincoln, Midtown and Battery tunnels.
The Port Authority of New York said the action was a precaution. Mobile phones can be used to detonate bombs remotely, as in last year's Madrid train attacks.
But New York's Mayor Michael Bloomberg questioned the wisdom of a move which prevents people making emergency calls.
"I don't know if it makes the most sense," AP news agency quoted him as saying. "Cell phones provide a measure of comfort."
Security was stepped up across New York City in the wake of the bombings in London last Thursday, which left at least 52 dead and 700 injured.
The Port Authority of New York and New Jersey, which runs the Holland and Lincoln tunnels, said the transmitters providing wireless services would remain shut off indefinitely.
Spokesman Tony Ciavolella said: "This was an initiative we put into place for the safety and security of the public."
The Metropolitan Transport Authority also suspended mobile services in the Battery tunnel to Brooklyn and Midtown tunnel to Queens on Thursday - but reinstated them on Monday.
A New York Police department spokesman said they would weigh the benefits of a disabled service against allowing drivers to call in if they spotted suspicious packages or activities.
The US Department of Homeland Security said the decision to cut mobile phone services was not made on the recommendation of the government, AP reports.
UK police do not believe calls to mobile phones were used to trigger the London bombs because the Underground does not have mobile phone reception.