ABCNews reported in 2013:
President Obama and Florida Sen. Marco Rubio both mentioned guest workers as part of their early outlines for immigration reform, but unions oppose what they’ve called “indentured” worker programs.
Further in the report:
While not mentioned in the outline, the [union position] subtext is that guest workers — perhaps working without healthcare or other benefits — could drive down salaries for native-born workers. Even existing guest worker programs should be reformed, according to the SEIU’s Medina. Since guest workers are tied to a single business through their visas, “employers use that to threaten and control workers,” he said.
A consistent argument of unions is that guest workers take work away from domestic workers, as stated in this Huffington Post story in 2013:
Critics of the guest worker program have argued that employers have relied too heavily on cheap foreign labor when millions of Americans are out of work.
Even in times of high unemployment, farmers have had a difficult time finding willing workers for farm jobs, while foreign workers see them as invaluable opportunities to earn significant income for their families.