The Senate Judiciary Committee will hear from Comcast Executive Vice President David Cohen and Time Warner Cable Executive Vice President Arthur Minson on Wednesday.

Comcast, the No. 1 U.S. cable operator, has announced plans to buy rival Time Warner Cable for $45.2 billion. Both are major broadband providers as well.

On the Senate panel will be Gene Kimmelman, head of Public Knowledge which is one of the most vocal opponents of the merger. Kimmelman was at the Justice Department's Antitrust Division when it approved the merger of Comcast and NBC Universal and stopped AT&T's proposed purchase of T-Mobile USA.

Comcast's proposed megadeal has raised eyebrows over the concentration it would give the merged company in key U.S. media markets.

To try to win approval for the deal, Comcast has pledged to divest 3 million subscribers so the combined customer base of 30 million would represent just under 30 percent of the U.S. pay television video market. A combined Comcast and Time Warner Cable would also have roughly one-third of the high-speed Internet market

Another witness speaking to the Senate panel is James Bosworth from Back9Network, an independent golf channel. The fifth witness is Richard Sherwin from Spot On Networks, a managed Wi-Fi provider. The sixth is Christopher Yoo, who teaches at the University of Pennsylvania Law School.

The hearing is unusual in that the Judiciary Committee is holding it rather than the committee's antitrust subcommittee, which is more common.

The proposed transaction is subject to approval by the U.S. Federal Communications Commission and the U.S. Justice Department.

(Reporting by Diane Bartz; editing by Andrew Hay)