Google and Amazon are invited. So are Apple and Twitter.

Consumer groups are not.

Nearly 30 of those groups have registered their criticism at being excluded from a U.S. Senate hearing on Wednesday addressing online consumer data privacy. The hearing, being held by the Senate Commerce Committee, includes witnesses from six of the biggest online and communications companies in the world, but no consumer advocates.

In a letter to South Dakota Sen. John Thune, the Republican chairman, and Florida Sen. Bill Nelson, the Democratic ranking member, the groups argue that allowing only industry groups to testify “all but ensures a narrow discussion, focused on policy alternatives favored by business groups.”

“Will,” the letter asks, “any of your witnesses recommend federal baseline legislation, heightened penalties for data breaches, the end of arbitration clauses, the establishment of a privacy agency in the U.S., techniques for data minimization, or algorithmic transparency to prevent the secret profiling of American consumers? These are all safeguards favored by many consumer privacy organizations that should be considered by Committee Members. How can members of the Committee develop sensible solutions if they are not even aware of the full range of options?”

In an emailed statement, Thune spokesman Ryan Wrasse said the Commerce Committee invited companies that are household names “in an effort to make the discussion about privacy more relatable.”

“We fully expect there will be opportunities for additional voices to be heard on this subject at future hearings,” Wrasse said.

The hearing comes amid increased scrutiny of how online giants are collecting and then using data on its users. The extent of that data became clearer with revelations that Cambridge Analytica used Facebook data to target voters in the 2016 presidential election.

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Jeff Chester, the executive director of the Center for Digital Democracy, one of the groups that singed on to the Thune/Nelson letter, said the extent of data that companies collect continues to expand. With mobile phones, companies have been able to “push the boundaries” to piece together identities and erode privacy.

“They’re making tens of billions of dollars, where digital data is gold – the new oil,” he said.

Faced with tougher regulations from the European Union and the state of California to protect consumer data, Google, Amazon and other industry groups now want the federal government to pass some regulations, Chester said. But Chester fears they wanted watered down regulations, not the tougher regulations in Europe and California.

“They want to head off those regulations and, in a way, get the weakest possible deal,” he said.

“It’s absurd,” he added. “The fact of the matter is, those companies are going to say the same thing.”

Besides Google, Apple, Twitter and Amazon, representatives from AT&T and Charter Communications will also testify.