The American Civil Liberties Union (search) and a dozen nonprofit groups are suing the government over new rules requiring organizations that receive money from a federal employees' charitable drive to check their staffs against terrorist watch lists.

The lawsuit against the Office of Personnel Management disputes a policy in the agency's Combined Federal Campaign (search) that requires participating charities to certify they don't knowingly employ people or contribute money to organizations found on the terrorist watch lists (search) of the United States, the United Nations or the European Union.

The CFC allows federal employees to have deductions taken from their paychecks and given to designated charities. It is the nation's largest workplace charity drive.

The fund raised almost $250 million for charities last year from about 1,345,000 federal employees. The money went to more than 10,000 participating nonprofits that support the country's health and education systems, the arts, the environment, children's services and religious institutions, the ACLU said.

The lawsuit filed in the U.S. District Court for the District of Columbia alleges the new requirements are unconstitutional.

The ACLU says the government didn't follow appropriate procedures in instituting the policy and argues the new rules are vague — not specifying, for example, how often participating charities must vet their employee and donation lists.

"Forcing charities to check their employees' names against a watch list will not make Americans any safer," said ACLU Executive Director Anthony Romero. "The CFC policy threatens to disrupt a crucial network of charities that are dedicated to promoting and protecting American lives and values."

OPM spokesman Edmund Byrnes said the agency would not comment and referred calls to the Justice Department, which is handling the lawsuit. The Justice Department also declined to comment, saying it had yet to review the case.

The lawsuit also charges that the government is trying to turn charities into an arm of law enforcement.

"The charities of America are not qualified and do not have the resources to be police agents," said Kay Guinane, an attorney with OMB Watch, a government accountability advocacy group. The group joined in the lawsuit.