Jeffrey D. Allred, Deseret News
Legislators meet at the Utah State Capitol in Salt Lake City Thursday, March 14, 2013.

SALT LAKE CITY — Utah prosecutors are dropping charges against four animal activists filed under a controversial law known as "ag-gag."

The activists from California and Maryland will still each face one misdemeanor count of criminal trespass, said Iron County Attorney Scott Garrett on Monday. Prosecutors received the case after the four activists pleaded not guilty last week. They decided to drop agricultural interference charges because officials from Utah's Circle Four Farms didn't want to pursue them, Garrett said.

Those counts came under a law that makes it a crime to conduct undercover investigations of slaughterhouses and factory farms. It has being challenged in court by activists who say it was designed to prevent exposure of unsafe practices.

Six other states have similar measures, but the only other person to face charges was also from Utah, according to Matthew Liebman, a lawyer from the Animal Legal Defense Fund, a group suing to strike down the law.

Police say the four activists from the Farm Animal Rights Movement drove onto private property at the hog farm in September and took pictures. Their lawyer says they were on a public roadway and only captured images of farm buildings, not workers or animals.

Attorney T. Matthew Phillips has said his clients wanted to retrace the pigs' path to a California slaughterhouse, not provoke an arrest. They are Sarah Jane Gage, 43, of Los Angeles; Robert Penney, 64, of Laguna Beach, California; Harold Weiss, 34, of Pasadena, California; and Bryan Monell, 50, of Mount Rainier, Maryland, according to court records.

Phillips didn't immediately return a message seeking comment Monday.

Circle Four Farms is part of Murphy-Brown LLC, the livestock production subsidiary of the world's largest pork producer, Smithfield Foods Inc. The Utah farm raises and markets about 1.2 million hogs per year and employs about 450 people.

Members of the Bethesda, Maryland-based Farm Animal Rights Movement want to end the use of animals for food, according to the group's website, and promote a vegan lifestyle with advertisements and occasional dramatic protests.