BGC Partners plans to make a hostile bid to buy rival GFI Group for $675 million, according to people familiar with the matter, after an effort to strike a friendly deal between the interdealer brokers foundered.

BGC, run by Cantor Fitzgerald chief executive Howard Lutnick, plans to launch a $5.25-a-share tender offer to GFI's shareholders as early as Wednesday morning, the people said. It is seeking to thwart GFI's planned sale to CME Group for $580 million in stock.