Shares of SES SA FDR /zigman2/quotes/202472664/delayed FR:SESG +0.92% tumbled 21% on Tuesday, a day after Federal Communications Chairman Ajit Pai said via Twitter that he would back a public auction to free up spectrum for 5G. Luxembourg-based satellite companies SES and Intelsat SA /zigman2/quotes/205500850/composite I +183.86% were lobbying for a private auction of the so-called C-band spectrum, used to deliver videos and radio programs to U.S. households. The FCC wants to free it up for carriers to bid on as 5G service gears up. Pai said the agency wants to make C-band spectrum available quickly for 5G and also must generate revenue for the government, saying the best way forward is an auction of 280 megahertz of the C-band. Intelsat shares plunged 40% on Monday.