Veteran consolidation critic Sen. Al Franken (D-Minn.) has written the heads of the agencies vetting the proposed Charter/Time Warner Cable merger, asking them to inspect the deal with a high level of scrutiny.

In the letter to FCC chairman Tom Wheeler and Attorney General Loretta Lynch dated Oct. 8, he said he remained concerned about the impact of "further consolidation" in what he called an already highly concentrated industry.

He said the regulators need to look hard at the merger candidate's public interest commitments to see whether they serve the public interest, are "reliable" and are the "Best way" of expanding access to broadband and cable services.

Franken is particularly concerned about rural areas. To that end, he said he appreciated Charter's commitment to providing high-speed access to those rural areas, but would prefer more details in the public interest statement on how it plans to do that.

He also said he was worried that, given the debt needed for the deal, the new company would not have the incentive, and resources, to expand rural broadband or fund other commitments.

He said it is "crucial" that the reliability of the companies' promises be examined, and balanced against the potential competitive harms.

Franken has his own bottom line test for further consolidation. He says it should only be allowed it it demonstrably improves broadband access and affordability, particularly for rural areas like many in Minnesota.

When asked whether the senator plans to oppose the deal, as he did Comcast/TWC, press secretary Michael Dale-Stein said  that the Senator had called for "high scrutiny" when the deal was first announced, continued to do so, and added that the timing of the letter was in response to the proposed public interest commitments in the deal.