"What is to stop them?" Grunes asked.
Comcast has agreed as part of this deal to shed 3.9 million cable-TV subscribers, selling some to Charter Communications Inc. and spinning others into a new publicly traded company.
As for the broadband business, "It looks a little bit like the Microsoft case," Grunes, now a Washington attorney, said of a combination of Comcast and Time Warner Cable.
The Justice Department sued Microsoft in the late 1990s, claiming its dominant PC operating system stifled competition in the Internet browser market. Microsoft settled the case.
Similarly, Comcast could use its market power in the broadband business to thwart online video services that compete with the company's legacy cable-TV service by making it expensive or difficult for those new services to stream video to people's homes, Grunes said. According to estimates, a combined Comcast and Time Warner Cable could control well over 30 percent of the nation's residential broadband market.
Also scheduled to testify is David Schaeffer, the chief executive officer of Cogent Communications, an Internet services company. Schaeffer told the New York Post in April that the deal would "allow Comcast to further extend its monopoly over its customers."
Matthew M. Polka, chief executive officer of a trade organization of small cable operators, and Patrick Gottsch, chairman of the Rural Media Group, are also scheduled to testify before the committee. U.S. Rep. Spencer Bachus (R., Ala.) chairs the committee.
C. Scott Hemphill, a Columbia University law professor who studies the interactions among innovation, competition, antitrust law, intellectual property and regulation, also will speak.
Comcast executive vice president David L. Cohen will represent the Philadelphia cable-TV giant. Time Warner Cable chief executive Robert D. Marcus, who will benefit from an $80 million golden parachute compensation package if the deal closes, also will testify.
The hearing will begin at 9:30 a.m. in the Rayburn Office Building.