European Commission investigators raided Twenty-First Century Fox’s London office on Tuesday, The Daily Telegraph reported.

Sources at the location told the newspaper that authorities were trying to be discreet and had been told to keep details of their mission confidential. The Telegraph reported that investigators will be on site through Wednesday and maybe Thursday.

Shares of Fox fell more than 1 percent in extended trading.

The raid comes amid Fox’s drawn out takeover of Sky, which has fallen under intense scrutiny by regulators at the U.K.’s Competition and Markets Authority.

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