The Clayton Antitrust Act modified the Sherman Antitrust Act by weakening the act by including labor unions as part of the definition of trusts. Specifically, the Clayton Act clarified and expanded upon the Sherman Act, making it more difficult for businesses to engage in anti-competitive practices and explicitly exempting labor unions and agricultural organizations from being considered illegal combinations or conspiracies in restraint of trade. This was significant because it aimed to protect the rights of workers to organize, which was not clearly addressed in the Sherman Act. So, the correct statement is:
It weakened the act by including labor unions as part of the definition of trusts.