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WASHINGTON (Reuters) - Republican Senator John Kennedy has joined his Democratic colleague Amy Klobuchar in calling on Facebook Inc Chief Executive Mark Zuckerberg to testify before Congress following reports that a political consultancy gained inappropriate access to data on millions of Facebook users.

In a joint letter, Kennedy and Klobuchar asked Senate Judiciary Chairman Chuck Grassley to hold a hearing with Zuckerberg and the chief executives of Alphabet Inc’s Google and Twitter Inc, reflecting mounting bipartisan concern in Washington about how the companies share personal user data.

“Facebook, Google, and Twitter have amassed unprecedented amounts of personal data and use this data when selling advertising, including political advertisements,” the senators wrote. “The lack of oversight on how data is stored and how political advertisements are sold raises concerns about the integrity of American elections as well as privacy rights.”

The letter came after reports this weekend that Cambridge Analytica, a political consultancy that worked on President Donald Trump’s campaign, gained inappropriate access to data on 50 million Facebook use.