US politicians pressed AT&T, Sprint, T-Mobile US and Verizon for answers about their network prioritisation policies, after a study found the operators slowed speeds for certain data services but not others.

In a letter, first spotted by Ars Technica, Senators Edward Markey, Richard Blumenthal and Ron Wyden asked operators how they decide what content to prioritise; whether customers are able to opt-in or out of traffic differentiation; and whether those choices impact the price of service.

The queries come during a battle over net neutrality regulations in the country and in response to a recent study based on data from network testing app Wehe, which found all four operators throttled speeds for a handful of services, including video streaming sites Netflix and YouTube.

Federal Communications Commission member Jessica Rosenworcel similarly responded to the report with concern at a regular monthly meeting, noting it “demonstrates that net neutrality matters and that companies, when they have the technical ability to censor and slow your traffic, the business incentive to do so and the legal right, they will go ahead and make it happen”.

Network management
However, Tom Sawanobori, CTO of industry association CTIA, last month refuted the findings, arguing in a blog that the differentiation Wehe picked up was the result of “basic wireless network management”. He added such practices save data for consumers without impacting experience.

Brendan Gill, CEO of network benchmarking company OpenSignal, in September noted an increase in video streaming had put a strain on mobile networks and US operators have turned to bandwidth limits to smooth out spikes in data traffic. But he said the company had yet to determine whether the practice actually yields the promised consumer benefits.