Unionists and immigrant rights activists are at once excited and apprehensive about the immigration law overhaul proposed by the Obama administration. A path to citizenship, though it will be arduous, could give some of the nation’s 11 million undocumented workers a chance to get their papers and become full participants in work and civic life. This could be a breakthrough for unions: every worker who becomes documented is a worker whose boss can no longer threaten to have her deported if she stands up for her rights on the job. But, as a pro-business trade-off, the law may also come with an expanded “guestworker” component. Historically, defenders of worker rights, including unions, have objected to guestworker programs, calling them “modern-day indentured servitude.” Guestworkers are tied to their employers on pain of deportation—making it hard for them to protest mistreatment or low pay, causing employers to hire them instead of U.S. residents….