Iowa Attorney General Tom Miller is joining a national effort to urge the U.S. Department of Justice to pursue a federal investigation into alleged price manipulation that’s raising the price of beef for consumers.

Miller and attorneys general in 10 other states sent a letter to U.S. Attorney General William Barr about possible price manipulation by meatpackers, resulting in higher than normal beef prices at grocery stores, according to a news release.

The pricing is a sign that meatpackers are using their ability to control the market to take advantage of the COVID-19 pandemic and consumer stockpiling, which may violate federal antitrust law, according to the release.

Four meatpacking companies control more than 80% of beef processing in the U.S., making it easier to manipulate prices. While beef costs in grocery stores are high, cattle prices are low and continue to dive, according to the attorney general’s office.

“We are specifically asking the Department of Justice to lead a thorough examination of the competitive dynamics of this industry,” according to the letter. “Now, more than ever, we need to dedicate our collective resources to promote competition and protect consumers.”

In addition to Iowa, the states signing the letter were Arizona, Colorado, Idaho, Minnesota, Missouri, Montana, Nebraska, North Dakota, South Dakota and Wyoming.