Amazon.com Inc. Chief Executive Jeff Bezos is willing to testify to a congressional panel investigating potential violations of U.S. antitrust law by big technology companies, according to a letter from an attorney representing Amazon.

The letter to members of the House Judiciary Committee said Amazon had cooperated with the panel's probe. "This includes making Jeff Bezos available to testify at a hearing with the other CEOs this summer," said the letter, signed by Robert Kelner of Covington and Burling LLP.

A copy of the letter was seen by Reuters.

The big four tech platforms -- Alphabet Inc's Google, Apple Inc, Amazon and Facebook Inc -- are under investigation by a House Judiciary Committee panel and the U.S. Justice Department. Meanwhile, the Federal Trade Commission is probing Facebook and Amazon and groups of U.S. state attorneys general are looking at Facebook and Google.

Kelner said in the letter that Amazon and the committee would need to "resolve a number of questions regarding timing, format, and outstanding document production issues, all necessarily framed by the extraordinary demands of the global pandemic."

Further, the letter also noted that Amazon had given the committee's antitrust panel large numbers of documents totaling more than 225,000 pages and notes that the committee has not given a "binding commitment" that the documents would be treated as confidential.

The committee did not immediately respond to a request for comment. 

The Wall Street Journal reported Friday that California is examining the retail giant's business practices, focusing partly on how Amazon treats independent sellers on its platform. Also on Friday, The New York Times reported that state investigators in Washington are reviewing Amazon's handling of third-party sellers on its site. The reports cited unnamed persons familiar with the matter.

Amazon and the state attorneys general in California and Washington did not immediately respond to requests for comment Saturday.

The state inquiries come amid heightened government scrutiny into big technology companies and their impact on competition and consumers. The U.S. Justice Department and the Federal Trade Commission are pursuing antitrust probes into Amazon, Google, Facebook and Apple.

California has been asking Amazon about the company's private label products and whether it uses the data from third-party sellers to inform which products it sells, according to the Times report, which noted that the inquiries in California and Washington do not appear to be in advanced stages.

Amazon (AMZN) used sensitive, confidential information about sellers on its marketplace, their products and transactions to develop its own competing products, according to a Wall Street Journal report in April. The company has denied such a practice and said it has a policy against it.