BERLIN — The German government is following up on media reports that coronavirus test centers across the country have overbilled authorities for the number of tests taken.

Germans are allowed one free “citizen’s test” per week to check if they are negative for coronavirus. They can use the result to be able to dine at outside restaurants, go shopping or visit cultural institutions.

In recent weeks, thousands of antigen tests centers for have popped up everywhere in cities and towns in empty store fronts, closed dance clubs or community centers. Several media have reported that test center operators are illegally billing for more tests than they actually take.

German Health Minister Jens Spahn tweeted Saturday that “anybody who uses the pandemic to enrich himself should be ashamed.” He noted that prosecutors in the western city of Bochum were investigating some suspected cases of fraud, but said that most providers were doing a professional job.