Blanchflower, David, Neil Millward, and Andrew Oswald. "Unionism and Employment Behavior." The Economic Journal, July 1991.
Uses British manufacturing employment growth to show that, between 1981 and 1984, unionized firms in the U.K. grew 3% slower than non-union firms. A review of an alternate data set finds that unionized firms grew faster between 1977 and 1978. The Thatcher government cited a predecessor study by the same authors as justification for anti-union policies. The authors argue, however, that "there is no systematic link between unions and employment growth."
Link (1989 working paper): http://www.nber.org/papers/w3180