Representative Ro Khanna, the California Democrat representing Silicon Valley, laid out his case against a sweeping ban of the social media platform TikTok on Sunday after opposing legislation that overwhelmingly passed the House last week, saying the bill would be ineffective.

The legislation passed the House, 352 to 65, on Wednesday, with Mr. Khanna among 50 Democrats, mostly from the progressive wing, who voted against it. He said the focus should be on enhancing data privacy laws rather than banning a social media platform.

“What is the actual evidence that you couldn’t pass a data privacy law or law banning data going to a foreign country, and get that done that way?” Mr. Khanna, one of the progressive Democrats, said on ABC’s “This Week.” “The frustration is that we have not been able to pass these data privacy laws. Those laws would also cover data brokers which are selling data to Chinese companies. This bill is not actually addressing that issue.”

Those who opposed the bill also cited concerns about violating Americans’ right to free speech and hurting small-business owners who rely on TikTok for their marketing and sales.

The legislation mandates that TikTok’s parent company, ByteDance, sell its U.S. assets within six months after the bill is signed into a law or face an outright ban in the United States. Supporters of the measure worry about the Chinese government gaining access to the data of roughly 150 million U.S. residents who use the video app and influencing the public debate in America by tweaking the app’s algorithms to its favor.

While recognizing the concerns raised by TikTok’s critics, Mr. Khanna said on Sunday that the security threats from the Chinese government could be tackled more effectively with “a narrowly tailored law” that forbids any transfer of private data of Americans to China and other foreign entities.