Concerned over a shortage of a key medication used to treat Lyme disease, Maine Sen. Susan Collins is calling on federal drug regulators to take immediate action.

Joined by Sen. Amy Klobuchar, D-Minn., Collins on Friday urged U.S. Food and Drug Administration Commissioner Dr. Margaret Hamburg to take steps to alleviate the shortage of doxycycline, an oral antibiotic used to treat Lyme disease and other infectious diseases.

In a letter to Hamburg, the senators said the shortage is especially worrying given that Lyme disease is most commonly contracted during May and June during peak tick season. The disease is transmitted through the bite of an infected deer tick.

Both Maine and Minnesota have high incidences of tick-borne illnesses. A record-high 1,100 Maine residents were diagnosed last year with Lyme disease, and public health officials have warned that the risk for Lyme has increased now that ticks have emerged for the season.

Nationally, nearly 30,000 cases of Lyme disease are reported annually, making it the sixth most commonly reported infectious disease in the United States.

“According to our state epidemiologist, the number of Maine residents diagnosed with Lyme disease continues to increase each year,” Collins said in a press release about the letter. “The antibiotic doxycycline is critically important for treating these patients, and it’s imperative that the FDA do all it can to help alleviate this shortage.”

Lyme disease can cause fever, chills and body aches, as well as later-stage and more serious problems including joint pain and neurological issues.

The FDA first reported a shortage of doxycycline on Jan. 18. Maine hasn’t yet experienced any shortages, according to the Maine Center for Disease Control and Prevention, which is monitoring supplies.

The shortage has led to significant price increases for doxycycline, potentially limiting patients’ access to the drug, the senators wrote in the letter.

“While we understand FDA has no authority to address the pricing of medications, shortages like this can have a severe impact on access to necessary care and underscore the importance of immediate action to ease shortages,” they wrote.

Last year, Klobuchar and Collins worked together on legislation to improve the FDA’s response to drug shortages. The law’s provisions require companies to provide early warning notification to the FDA of any developments that could result in a drug shortage.