WASHINGTON — The FDA proposed a rule Friday that would require the largest food businesses in the U.S. and abroad to take steps to prevent contamination attempts intended to inflict massive harm to public health. The rule is required under the Food Safety Modernization Act.

While the FDA is unaware of any attempt of this kind being made, the rule is intended as a preventive measure.

Under the proposed rule, a food facility would be required to have a written food defense plan that addresses significant vulnerabilities in its food production process. Facilities would have to identify and implement strategies to address these vulnerabilities, establish monitoring procedures and corrective actions, verify that the system is working, ensure that personnel assigned to the vulnerable areas receive appropriate training and maintain certain records.

There are exemptions based on the size of the business, sales and certain types of operations such as holding or repacking food, with certain exceptions. The rule doesn’t apply to farms and food for animals. The FDA seeks public comment through March 31. Implementation would range from one to three years, based on business size.