Invoking security concerns, President Bush has issued an executive order barring union representation at United States attorneys' offices and at four other agencies in the Justice Department.
Although federal law bans strikes by federal employees, White House officials said Mr. Bush had issued his order out of concern that union contracts could restrict the ability of workers in the Justice Department to protect Americans and national security.
The order, issued on Jan. 7, has angered unions, which say the president is exploiting the terrorist attacks of Sept. 11 to pursue a campaign against unions.
The order bars representation for more than 500 workers at the United States attorneys' offices, the criminal division, the National Drug Intelligence Center, the Office of Intelligence Policy and Review and the National Central Bureau of Interpol.
The associate director for collective bargaining at the American Federation of State, County and Municipal Employees, Steven Kreisberg, said unionization in no way threatened national security.
"We're outraged by this," said Mr. Kreisberg, whose union represents more than 300 employees in the Justice Department, including secretaries, file clerks and messengers.
"A lot of these Justice Department workers have been members of unions for 20 years," he said, "and there's never been an allegation of a problem. It's a very cynical use of the Sept. 11 tragedy by an antiunion administration."
A spokeswoman for the White House, Anne Womack, said previous presidents had barred other classes of federal workers from unionizing by invoking the national security exemption in the law that gives federal employees the right to unionize.
"The legislation," Ms. Womack said, "recognizes that a unionized work force is not always appropriate for certain agencies or subdivisions of government, including employees who engage in investigation, intelligence, counterintelligence or national security."
The order has widened a rift between Mr. Bush and labor. Last week, unions condemned his naming Eugene Scalia, son of Justice Antonin Scalia of the Supreme Court, as Labor Department solicitor after failing to win Senate approval. As a corporate lawyer, Mr. Scalia had enraged unions by saying an ergonomics regulation from the Clinton administration intended to reduce workplace injuries was based on "quackery" and "junk science."