LOS ANGELES — A U.S. Customs official said that the government is entering the "penalty phase" as part of its enforcement of the advance manifest filing rule.

The anti-terror measure requires that shipping lines and freight consolidators electronically file a complete description of U.S.-bound shipments at least 24 hours before the cargo is loaded on a vessel in a foreign port. The rule, along with other measures adopted since the September 11 attacks, are designed to prevent terrorists from smuggling weapons of mass destruction into the U.S.

Customs implemented the so-called 24-hour rule last fall and after a transition period began enforcing it on Feb. 2. The agency this spring has been issuing "no load" orders for shipments in foreign ports that are not accompanied by proper cargo classifications or shipper-consignee descriptions.

The rule also gives the government the authority to hit shippers with monetary penalties for failure to provide 15 key data elements on U.S.-bound cargo. "We are now entering the penalty phase," John Heinrich, interim director of field operations for Southern California, on Monday told a security conference sponsored by the National Industrial Transportation League.

As it has done from the beginning of its enforcement effort, Customs will take a "reasoned and measured approach" in dealing with offenders. "We will go after the egregious offenses. There are some people who just don't get it," Heinrich said.