The ACLU released documents this week, obtained through a lawsuit against the Maryland State Police, indicating that Maryland State Police troopers had gone undercover to spy on protest meetings -- particularly meetings to plan demonstrations against the death penalty and protests outside Fort Meade, the headquarters of the National Security Agency.

O'Malley issued a statement Friday saying the spying took place under his predecessor, Robert Ehrlich, and promising his administration would "take seriously" possible threats against public safety, The Baltimore Sun reported.

O'Malley is a Democrat. Ehrlich, a Republican, said Friday on WJZ-TV, Baltimore, he was "sympathetic" to the public's right to assemble without being monitored, but he said state troopers "bring discretion with them to their jobs every day, so their job on a daily basis obviously is to weigh the relative value of intelligence they've received and to make decisions accordingly."

Maryland Sen. Ben Cardin, a Democrat and a member of the U.S. Senate Judiciary Committee, said the United States "cannot allow police activity that is intended to discourage dissent by Americans who may disagree with certain government policies."