Another point of discussion is the proportion of trade unionists. Opponents say that after the PLA, business leaders must hire their workers through unions and unionized workers are the majority of those working on PLA projects, although non-unionized workers make up the majority of construction workers.  Estimates of the proportion of non-unionists cited by PLA opponents are about 85%, based on figures from the Us Department of Labor Bureau of Labor Statistics and more recent data put the figure at 86.9%.  This figure is disputed by Denas, who indicates that the figures of opponents of the PLA are misleading and are based on census data that included an overly broad concept of a construction worker.  According to a 2010 Cornell University study cited by Mary Vogel, Executive Director of the Construction Institute, 60% of construction trades are unionized in Massachusetts.  Since its inception in 1998, The Construction Institute, a non-profit organization, has focused on the needs of the construction union sector in Massachusetts. The first uses of Project Labor Agreements in the United States date back to several dam projects in the 1930s, including the Grand Coulee Dam in Washington, the Shasta Dam in California and the Hoover Dam in Nevada.  Modern PLPs developed particularly from those used in the construction sector during the Second World War, at a time when demand for skilled labour was needed, construction unions controlled 87% of the national market and public construction spending had increased significantly in a short period of time. These early PPPs focused on setting standard rates of pay and preventing work stoppages.  Cape Canaveral in the 1960s, Disney World from 1967-71 and Trans-Alaska Pipeline from 1973 to 1977.   At that time and thereafter, the union share of the construction industry declined rapidly as construction users sought open competition. In the 1980s, non-unionized contractors claimed more than 80% of construction work in a large number of companies, with some differences in different parts of the country.  Studies have shown that PROJECT owners and local PLA communities have advantages and penalize contractors and non-union workers.
A 2009 study by Fred B. Kotler, J.D., associate director of Cornell University School of Industrial and Labor Relations, found that there was no evidence that PMAs discriminate pending employers and workers, limit the number of bidders and increase construction costs.  In a 2009 report by Dale Belman of Michigan State University; Matthew M. Bodah of the University of Rhode Island and Peter Philips of the University of Utah said that instead of increasing costs, the agreements would bring benefits to the community. According to your report, the cost of the project is directly related to the complexity of a project, not to the existence of an agreement. They found that AEPs are not suitable for all projects, but some projects are good candidates for their use, such as very complex construction projects.  Studies have also been conducted on how GPs can benefit local communities by hiring aboriginal people. In a paper that focused on whether the AEPs met local hiring targets for projects developed by the District Community College of Los Angeles (LACCD), the District of Los Angeles Unified (LAUSD) and the City of Los Angeles, the author found that the 30% local rent target set by the PLA has been met.  The Boston Harbor inlagiverumde project, which began in the 1980s, has been at the centre of the debate on the legality of LTAs.   When the Massachusetts Water Resources Authority decided to use a PLA for the project that involved unionized workers the Associated Builders and Contractors of Massachusetts/Rhode Island, Inc.