Tony Romo's contract with the Dallas Cowboys was structured in a way that prevents the team from applying their franchise tag in 2014.
That explains why the Cowboys are so interested in extending the quarterback's contract.
According to Ian Rapoport of NFL Network, Romo’s contract extends beyond 2013 by three years. Thus, Romo will become a free agent in 2014 not by the expiration of the deal, but by the voiding of the final three years.