Sen. Al Franken (D-Minn.) is a vocal critic of the proposed merger between Comcast and Time Warner Cable. (Lauren Victoria Burke/AP)

Sen. Al Franken (D-Minn.) has become Capitol Hill's loudest opponent of Comcast's bid for Time Warner Cable. Now, he's trying to root out like-minded critics from Silicon Valley.

In a letter to the trade group Computer & Communications Industry Association, Franken asked for the group's opinion on the $45 billion merger. If approved by federal regulators, Comcast would wind up with 40 percent of the broadband Internet market. Franken said that's too much power in the hands of a single company, which could act as a powerful gatekeeper for Internet content and services into U.S. homes.

"Your organization includes companies from many sectors of our communications and Internet economy, including industry leaders in search, social networking, e-commerce  and music and video content delivery. All of these organizations depend on broadband networks to operate," Franken wrote in his letter to CCIA President Ed Black. CCIA's members include Google, Facebook, eBay, Aereo and Yahoo.

Comcast and Time Warner Cable said they have voluntarily shed subscribers to keep their size at a competitive level. They have also said that Internet access rules will keep them from discriminating against video competitors online such as YouTube or Netflix.

But Franken's drumbeat of attention on potential consumer harms from the deal has caught the attention of media and consumer advocates. Franken has emerged as a sort of informal investigator on the merger, even though Congress doesn't officially review the deal. The government agencies responsible for reviewing the deal are the Justice Department and Federal Communications Commission. But Franken's probing questions of Web firms such as Netflix have unearthed new insights — and new opponents.

Netflix executives last week said in letters to shareholders and Franken that they opposed the merger. CEO Reed Hastings and Netflix's vice president of global affairs wrote that consumers would be harmed if Comcast controls more than 40 percent of all broadband Internet subscriptions and 30 percent of cable subscriptions. Netflix alleges that Comcast forced it to pay extra fees to ensure their streaming videos would be delivered smoothly into homes.

Public interest groups say television programmers, Web firms and other cable companies are reluctant to speak out critically against the merger for fear of retribution. In a hearing last month, Sen. Amy Klobuchar (D-Minn.) said several independent programmers told her they were concerned about the merger but were also afraid of speaking out against the deal.

In his letter to CCIA, Franken asked:

  1. First, do you believe that Comcast’s proposed acquisition of Time Warner Cable would harm the public interest?
  2. Second, in your view, what impact will the deal have on competition in relevant markets, and, ultimately, on consumers?
  3. Finally, please provide any other relevant views, including any thoughts you have about arguments made in the Public Interest Statement that Comcast recently filed with the FCC or in the testimony that Comcast and Time Warner Cable recently provided to the Senate Judiciary Committee.