Comcast Corp. is using rulings from Washington’s federal appeals court to try to allay antitrust concerns of lawmakers over the company’s proposed merger with Time Warner Cable Inc. The deal would create the nation’s largest cable and broadband Internet service provider.

David Cohen, Comcast’s executive vice president, testified on Capitol Hill today that the companies are willing to lose a combined 3 million customers—leaving the merged companies with 30 million customers—to bring them underneath a “30 percent” rule that was the subject of two court rulings.