<P> However, Mayer has written that it was precisely unions' opposition to NAFTA overall that jeopardized organized labor's ability to influence the debate on labor standards in a significant way . During Clinton's presidential campaign, labor unions wanted NAFTA to include a side deal to provide for a kind of international social charter, a set of standards that would be enforceable both in domestic courts and through international institutions . Mickey Kantor, then U.S. trade representative, had strong ties to organized labor and believed that he could get unions to come along with the agreement, particularly if they were given a strong voice in the negotiation process . </P> <P> When it became clear that Mexico would not stand for this kind of an agreement, some critics from the labor movement would not settle for any viable alternatives . In response, part of the labor movement wanted to declare their open opposition to the agreement, and to push for NAFTA's rejection in Congress . Ultimately, the ambivalence of labor groups led those within the Administration who supported NAFTA to believe that strengthening NAFTA's labor side agreement too much would cost more votes among Republicans than it would garner among Democrats, and would make it harder for the United States to elicit support from Mexico . </P> <P> Graubart writes that, despite unions' open disappointment with the outcome of this labor - side negotiation, labor activists, including the AFL - CIO have used the side agreement's citizen petition process to highlight ongoing political campaigns and struggles in their home countries . He claims that despite the relative weakness of the legal provisions themselves, the side - agreement has served a legitimizing functioning, giving certain social struggles a new kind of standing . </P> <P> Unions have recently been engaged in a developing field of transnational labor regulation embodied in corporate codes of conduct . However, O'Brien cautions that unions have been only peripherally involved in this process, and remain ambivalent about its potential effects . They worry that these codes could have legitimizing effects on companies that do not actually live up to good practices, and that companies could use codes to excuse or distract attention from the repression of unions . </P>

The percentage of the u.s. workforce belonging to unions has been increasing since the 1950s