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WASHINGTON (Reuters) - Facebook Inc Chief Operating Officer Sheryl Sandberg has tentatively agreed to testify before a U.S. House committee on Oct. 29 about the company’s plan for a digital currency, but the panel will not schedule the hearing until Chief Executive Mark Zuckerberg commits to appear by January, a congressional source said on Thursday.

The House of Representatives Financial Services Committee, which is seeking the testimony from Facebook executives, did not immediately respond to a request for comment. The panel’s plans were first reported by The Information technology news website.

Facebook shocked regulators and lawmakers with its announcement in June that it was hoping to launch a digital coin called Libra in 2020.

Policymakers and financial watchdogs at home and abroad are concerned about the effect of widespread adoption of Libra by the social media company’s 2.38 billion users on the global financial system.

“Facebook’s plans raise serious privacy, trading, national security, and monetary policy concerns, not only for Facebook’s over 2 billion users, who will have immediate access to these products, but also for consumers, investors and the global economy,” House Financial Services Committee Chairwoman Maxine Waters said at a hearing on Libra in July.

Waters has called on Facebook to stop implementation of the cryptocurrency until regulators and Congress can enact a legal framework.