The US Conference of Catholic Bishops has become the latest religious group to call on McDonald's to push for its tomato suppliers to pay higher wages.
Most of McDonald's US tomatoes come from Florida
With most of McDonald's US tomatoes coming from Florida, the bishops want the firm to broker a deal between the state's growers and main pickers union.
The call comes after Yum! Brands, owner of Taco Bell, Pizza Hut and KFC, achieved a similar agreement last year.
Florida's tomato pickers are chiefly Hispanic, Haitian and Mayan immigrants.
The Catholic move comes after similar action from the Prebyterian Church, United Church of Christ, and National Council of Churches.
Bishop Nicholas DiMarzio, head of the Conference of Catholic Bishop's Domestic Policy Committee, has sent an open letter to McDonald's to put across its thoughts.
The bishops want McDonald's to bring its purchasing power to bear
He told McDonald's that with "substantial purchasing power, you can insist that your produce suppliers meet high ethical standards in how they treat their workers".
McDonald's spokesman William Whitman said the company has required suppliers to comply with its code of conduct on workers' health, safety and legal rights since it was established in 1993.
"We believe that all employees, including those who work for our business partners, should be treated with dignity and respect in every aspect of the employment relationship," he said.
Florida's immigrant farmworkers are represented by the Coalition of Immokalee Workers.
This group boycotted Yum! Brands outlets for four years before an increased pay deal was brokered last year.