After months of speculation about changes to U.S. temporary worker visa programs, President Donald Trump signed an executive order on Tuesday that aims to retool the H-1B program from a lottery to a merit-based system, as part of a “Buy American, Hire American” initiative also overhauling federal procurement procedures.

Trump's order begins a 220-day review process in which federal agencies will review and propose changes to the H-1B program that would restrict the program to only workers with the most advanced skills.

Immigration attorneys have spoken at length about how changes to the visa program, intended for foreign professionals with highly specialized skills, could particularly hurt the technology industry. Many of Silicon Valley's tech stalwarts are among the most frequent users of H-1B workers, and have opposed overhauling the system. Reports, including by The New York Times, however, have found that the program increasingly has been dominated by outsourcing companies based abroad rather than directly by employers. Critics say visas are going to lower-paid workers who are undercutting wages of some American workers.