New York Attorney General Investigating Possible Broadband Speed Overcharges Verizon, Cablevision and Time Warner are all involved in the probe.

The New York attorney general is probing whether three major Internet providers could be short-changing consumers by charging them for faster broadband speeds and failing to deliver the speeds being advertised, according to documents seen by Reuters.

The letters, which were sent on Friday to executives at Verizon Communications Inc, Cablevision Systems Corp and Time Warner Cable Inc, ask each company to provide copies of all the disclosures they have made to customers, as well as copies of any testing they may have done to study their Internet speeds.

"New Yorkers deserve the Internet speeds they pay for. But, it turns out, many of us may be paying for one thing, and getting another," New York Attorney General Eric Schneiderman said in a statement.

Time Warner Cable spokesman Bobby Amirshahi said in a statement: "We're confident that we provide our customers the speeds and services we promise them and look forward to working with the AG to resolve this matter."

Cablevision spokesman Charlie Schueler said the company's Optimum Online service "consistently surpasses advertised broadband speeds, including in FCC and internal tests. We are happy to provide any necessary performance information to the Attorney General as we do to our customers."

Verizon declined comment, saying it had not yet seen the letter.

The probe by the attorney general is particularly focused on so-called interconnection arrangements, or contractual deals that Internet service providers strike with other networks for the mutual exchange of data.

In the letters, the office says it is concerned that customers paying a premium for higher speeds may be experiencing a disruption in their service thanks to technical problems and business disputes over the interconnection agreements.

A 2014 study by the Measurement Lab Consortium, or M-Lab, found that customers' Internet service tended to suffer at points where their broadband providers connected with long haul Internet traffic carriers including Cogent Communications Group Inc.

"Internet service provider interconnection has a substantial impact on consumer Internet performance - sometimes a severely negative impact," the study said, adding that business relationships rather than technical issues were often at the root of the problem.

A spokesman for the attorney general's office said the findings in the 2014 study, coupled with consumer complaints and internal analysis, prompted the inquiry into the Internet speeds.

Some of the letters also raise questions about speeds delivered by Time Warner Cable and Cablevision to consumers over "the last mile," a term that refers to the point where a telecommunication chain reaches a retail consumer's devices.

(Reporting by Sarah N. Lynch; Editing by Peter Cooney and Christian Plumb)