WASHINGTON (Reuters) - The U.S. Justice Department said on Friday it has filed a lawsuit alleging that pharmacy chain operator Walgreens knowingly filled millions of prescriptions that lacked a legitimate medical purpose.

If found liable, Walgreens, which is one of the country's largest pharmacy chains with over 8,000 pharmacies across the U.S., could face civil penalties of up to $80,850 for each unlawful prescription, the Justice Department said in a statement.