WASHINGTON, Nov 29 (Reuters) - The U.S. Department of Agriculture said on Tuesday it will extend for up to 90 days a trial program that allows six U.S. pork plants to operate faster processing-line speeds while collecting data on how the speeds affect meatpacking workers.

The decision is a win for major meat companies like Tyson Foods and JBS SA, and their farmers, at a time when both are losing money. Some activist groups like Food & Water Watch had opposed the program as a risk to food safety.

The plants, including one in Nebraska owned by Tyson and another in Illinois run by JBS's Swift Pork Company, were allowed to accelerate line speeds last year under a trial that required them to also implement worker safety measures under agreements with labor unions or worker safety committees.

Companies were eligible to participate in the trial because they had sped up processing speeds under a Trump-era rule that removed speed limits for hog slaughtering facilities. A judge in 2021 invalidated that rule after the United Food and Commercial Workers (UFCW) union, which represents many meatpacking workers, sued the USDA over worker safety concerns.

Tyson declined to comment. JBS and UFCW did not immediately respond to requests for comment.

Plants in the trial were also assigned to collect data on how line speeds affect workers and share it with the U.S. Occupational Safety and Health Administration.

On Tuesday, the agency said that data collected so far was not sufficient to assess the impact on workers and that further data and a study would be commissioned in the coming 90 days.

Nearly 40% of the 74 million hogs in the U.S. are within 100 miles of the six plants, making them vital to processing supplies, according to Republicans on the U.S. Senate Agriculture Committee who had warned that without USDA action, pork prices could rise and demand for hogs could fall.

(Reporting by Tom Polansek in Chicago and Leah Douglas in Washington; Editing by Bernadette Baum)