Facebook Inc. FB, +0.42% CEO Mark Zuckerberg won't appear before U.K. lawmakers who summoned him following a firestorm over how the company handled people's data. "Facebook fully recognizes the level of public and Parliamentary interest in these issues and support your belief that these issues must be addressed at the most senior levels of the company by those in an authoritative position to answer your questions," the social-media giant said in a letter, according to multiple published reports. "As such Mr. Zuckerberg has personally asked one of his deputies to make themselves available to give evidence."