GMLAs typically restrict the majority of employment on the project to only those workers whom unions are willing to refer to the project. The negative impact of GMLAs falls heavily on nonunion companies, small companies, and disadvantaged businesses. For instance, in 1998, Congress heard testimony from women and minority-owned businesses that were excluded from contracting opportunities by GMLAs. GMLAs effectively force open-shop contractors and their employees to unionize without regard to their preferences or an opportunity to vote. Furthermore, GMLAs force union contractors to work under different work rules and other contract terms that government bureaucrats have negotiated, rather than under the existing labor contracts that they or their agents have negotiated.
Organized labor argues that GMLAs are a legitimate and proper use of federal power.
GMLA supporters also argue that the 1993 Supreme Court Boston Harbor decision permits the federal government to mandate such agreements. The government should not force contractors to hire a certain group of workers or to exclude a certain group of contractors from bidding on public projects. The supposed benefits of GMLAs are somewhat illusory. The Boston Harbor decision was, in fact, very narrow. It did not involve a federal contract.