WASHINGTON — Small tech companies, consumer groups and many celebrities have been up in arms for weeks about a proposal at the Federal Communications Commission to dismantle landmark rules that guarantee an open internet.

But in one speech, Ajit Pai, the chairman of the agency, called the complaints “hysteria” and “hot air.” In another, he dismissed criticism that by pushing the change, he was doing the bidding of companies like Verizon, his former employer. He joked that his nightmare scenario would be refereeing a dispute between Verizon and Sinclair Broadcasting, another company he has been accused of helping with his policies.

“How do you choose,” he said, “between a longtime love and a newfound crush?”

The agency was expected to vote on Thursday to dismantle the so-called net neutrality rules, which prohibit internet service providers from blocking or charging websites for higher quality delivery to consumers. It would also dial back the stance established during the Obama administration that broadband should be regulated like a utility. The three Republican commissioners, including Mr. Pai, have said they will vote for the proposal, outnumbering the two Democratic commissioners.

Passing the plan would be the biggest victory in Mr. Pai’s eventful 11-month tenure as the head of the F.C.C. Under his leadership, the agency has already opened the door for more media mergers, curtailed a high-speed internet program for low-income families and allowed broadband providers to raise rates to business customers.