The New York state attorney general's office has sent letters to Verizon, Time Warner Cable, and Cablevision suggesting that the Internet speeds they deliver to consumers don't match what the companies are promising.

The letters, sent Friday by Senior Enforcement Counsel Tim Wu, say the AG's office "is concerned that, for reasons substantially within [the ISP's] control, consumers may not be experiencing the speeds advertised." Here are links to the letters to Verizon, Cablevision, and Time Warner Cable.

The letters claim that interconnection disputes may be causing slowdowns, but they do not point to any specific disputes or offer any evidence that the ISPs' speeds aren't as advertised. When we asked AG Eric Schneiderman's office for more specifics, we were told that the investigation was spurred by "complaints from customers," internal analysis, and a one-year-old report from the Measurement Lab Consortium. We wrote about that report at the time it came out, but the situation has changed significantly since then because of new federal rules.

The letters make a series of information requests and remind the ISPs that "the Attorney General has the authority to commence legal action to enjoin deceptive, fraudulent or illegal business practices, and to obtain restitution, penalties and costs whenever a business is engaged in deception, fraud or illegality."

There's no question that interconnection disputes between ISPs and other companies can affect consumer broadband quality. Even if speeds are fast within an ISP's network, interconnection problems can harm the connection between an ISP and Internet content that its customers try to access.

Netflix video was slowed down for months as a result of disputes with ISPs. But Netflix's disputes with the major ISPs including Verizon and Time Warner Cable were settled more than a year ago, with Netflix agreeing to pay for direct connections to the broadband providers' networks.

The Federal Communications Commission has taken action to prevent interconnection problems from harming consumers, with net neutrality rules that allow the FCC to intervene when contract disputes affect Internet quality. Several disputes were resolved just as the rules took effect in June of this year.

The New York AG's letters hint that the office believes disputes are still harming customers. The AG's office said it is "specifically concerned about disruptions to the consumer experience caused by interconnection disputes, and also the possibility that interconnection arrangements may in some instances render irrelevant any benefit of paying for a 'premium' option." If consumers pay for higher speeds but don't actually get the promised increases, they may be victims of deceptive advertising, the AG's office said.

The ISPs denied any shenanigans. “Verizon is confident in the robust and reliable Internet speeds it delivers to subscribers," Verizon told Ars. "We look forward to working cooperatively with the Attorney General’s office."

According to Reuters, Cablevision said its Internet service "consistently surpasses advertised broadband speeds, including in FCC and internal tests." TWC also said it is confident that it provides customers the speeds and services it promises.

The FCC's Measuring Broadband America report last year found that Verizon DSL offers 83 percent of its advertised speed during peak usage periods, below the 91 percent average for DSL-based services. DSL speeds vary widely, with homes further away from ISP infrastructure getting lower speeds due to distance limitations.

Verizon's fiber customers, on the other hand, generally receive higher speeds than they pay for, as do Cablevision customers, the FCC said. TWC customers received between 94 percent and 101 percent of advertised download speeds during peak times, according to the FCC data.

This data, based on speed tests, may not account for interconnection disputes that harm specific Internet services rather than Internet access in general.

That data also only measures speeds within an ISP's network, rather than speeds from a consumer's home to the rest of the Internet, a representative of the NY AG's office told Ars.The AG wants to find out whether a 300Mbps service, for example, is actually better than a 50Mbps service, the person said.

The information New York is requesting from ISPs includes subscriber data broken down by speed tier, disclosures made to broadband customers about actual or expected speeds, substantiation of speed claims, and complaints from customers about discrepancies between actual and expected speeds. The AG's office also asked for copies of all Internet interconnection agreements that the ISPs have with other companies and details on any incidents since January 2013 in which interconnection partners requested additional capacity but were not given the capacity within 90 days.