SAN DIEGO -- The union that represents Customs and Border Protection is asking for an official directive that would allow inspectors to wear face masks on the job to protect against swine flu.

The National Treasury Employees Union said Thursday that two customs inspectors at San Ysidro were told by their supervisors to remove their masks this week.

Harold Washington, the union's Local 105 president, says they were given no explanation for the supervisors' orders. Earlier this week, officials told staff to use masks and gloves if they wanted.

Agency spokesman Vince Bond has said booth duty officers can wear masks when dealing with travelers who have obvious signs of illness.