When Zucker tried to defend the networks' actions and said NBC has ordered seven independent shows for next fall, Franken interrupted, "Come on."
Franken also confronted Roberts about his promise to make programming available to competitors.
Roberts has insisted that current FCC rules are sufficient to protect consumers.
Showing a giant poster with a quote from one of Comcast's filings with the FCC over a dispute with the NFL, Franken pointed out that Comcast used the argument that the FCC was not "equipped or constitutionally empowered" to assess program access, carriage and pricing decisions.
"You told me to my face that these rules would protect consumers," Franken said. "But your lawyers had just finished arguing in front of the commission that it would be unconstitutional to enforce those rules."
Roberts disputed the exact issue he and Franken were discussing in his Senate office a week ago. Roberts said he thought they were talking about program access, not program carriage.
But Franken cut him off.
"How are (the people of Minnesota) to trust you when you come in and say to my face something you know is not true, or that you don't know--I don't know which one is worse--how are the people of Minnesota supposed to trust you?"
Sen. Arlen Specter (D-Penn.) suggested setting up a lengthier discussion outside of the hearing room to clear up the misunderstanding.
Franken agreed to the meeting, but did not let up on his attack.
To Roberts, he said, "You confirmed you had gone after the very rules you say will protect consumers...It's very hard to trust you guys from my point of view."