A Friday letter from Amazon to members of Congress looking into the company’s third-party seller practices was “unacceptable,” House Judiciary Committee Chairman Jerry Nadler (D-NY) tweeted Saturday.

At issue is an Amazon executive’s testimony at a hearing last July, where he said the company doesn’t access information from third-party sellers on its platform to make competing items. But the Wall Street Journal reported last month that Amazon employees regularly used information from the sellers to develop the company’s private-label products.

“Members from both parties have serious questions about Amazon’s business practices and its honesty with the Committee,” Nadler tweeted. “We will not permit stonewalling of our investigation, by Jeff Bezos or anyone.”

Amazon vice president of public policy Brian Huseman wrote in the letter that the company was “prepared to make the appropriate Amazon executive available,” to the committee, but did not mention Bezos. Huseman added that the company was investigating the claims made in the WSJ article.

“We disagree strongly with any suggestion that we have attempted to mislead the Committee or not been cooperative with the investigation,” Huseman wrote in the letter, which was addressed to Nadler and members of the House antitrust subcommittee.

Members of Congress have threatened to subpoena Bezos, an idea that Rep. David Cicilline (D-RI), chairman of the antitrust subcommittee repeated in a tweet on Friday.

“No one is above the law, no matter how rich or powerful,” Cicilline tweeted. “We have asked Mr. Bezos to testify before the US Congress about Amazon’s troubling business practices and false statements, and we expect him to do so. Whether he does so voluntarily or by subpoena is his choice.”