Federal regulators are poised to block EchoStar Communications Corp.'s $18 billion acquisition of rival Hughes Electronics Corp. in a vote that could take place as early as Monday, people familiar with the matter told The Wall Street Journal. Barring a major, last-minute concession from the two satellite-television providers -- a prospect that many industry officials over the weekend said still was possible -- at least three of the four members of the Federal Communications Commission are set to cast votes rejecting the deal, according to people knowledgeable about the matter. FCC Chairman Michael Powell is among those opposing the...