The Food and Drug Administration threatened Friday to take action to seize or block the sale of high-iodine eggs that a Pennsylvania firm claims can help reduce artery-clogging cholesterol.

In a letter sent to C.R. Eggs Inc. of King of Prussia, Pa., the FDA said it wants the firm to withdraw Heartland's Best eggs from the market "because of serious health concerns created by excessively high levels of iodine."Some studies have shown that increasing iodine intake appears to lower the levels of harmful cholesterol in the blood. To produce Heartland's Best eggs, hens are given a feed supplement that contains kelp, an iron-rich type of seaweed.

C.R. Eggs failed to comply with a previous FDA request, issued Dec. 24, to stop marketing the eggs.

Robert Fuhrman, president of C.R. Eggs, said in a statement that he plans to respond to the FDA's concerns "in a responsible and cooperative manner," and will meet with agency officials next week.