NEW YORK (Reuters) - Mylan NV said on Tuesday that U.S. consumers may have difficulty getting EpiPen prescriptions filled after manufacturing problems constrained supply, but the drugmaker did not say there was a shortage of its emergency allergy treatment.

This was Mylan’s first acknowledgment of possible U.S. supply issues following reports of EpiPen shortages in Canada and Britain last month.

Shares of Mylan, which is due to report quarterly financial results on Wednesday, fell 2 percent to $35.37.

Food allergy groups have been pressing U.S. regulators for answers after more than 400 people in 45 states told advocacy group Food Allergy Research & Education (FARE) that they have had trouble getting prescriptions filled for the potentially lifesaving autoinjectors of the drug epinephrine.

Still, the U.S. Food and Drug Administration said it does not believe there is a shortage.

“Mylan has continued to report adequate supply of EpiPens in the U.S.,” FDA Press Officer Theresa Eisenman said in a statement. “Occasionally pharmacies report local supply issues, however these are usually temporary and involve distribution issues and resolve when the pharmacy is able to reorder from their distributor.”

Last week, the American Society of Health-System Pharmacists (ASHP), which has different criteria for what constitutes a shortage than the FDA, added EpiPen, a lower dose version called EpiPen Jr, and Mylan’s own generic versions of those products to its list of drugs in short supply in the United States.

Mylan, which had declined to comment about possible U.S. EpiPen shortages for nearly a month, on Tuesday said it notified the FDA a few months ago of “intermittent supply constraints” due to delays at its manufacturing partner Pfizer Inc.

Mylan said it is currently receiving “continual” supply from Pfizer unit Meridian Medical Technologies, which produces all EpiPens sold globally at a single plant near St. Louis, Missouri.

“Supply levels may vary across wholesalers and pharmacies,” Mylan spokeswoman Lauren Kashtan said in an email. She said patients having trouble getting an EpiPen should call 800-796-9526 for assistance.

“There’s a problem out there. The FDA may not be fully aware of it because the companies that manufacture and distribute the EpiPen are not saying anything,” FARE Chief Executive Dr. James Baker said. “We’ve got people who literally can’t fill their prescriptions.”

Pfizer said it is currently shipping EpiPens and that they have been increasing over the last few months. It said April shipments exceeded projections, but the company did not disclose those projections.

Meridian Medical has been hit by a series of manufacturing problems. In March 2017, Mylan recalled tens of thousands of devices after complaints that some had failed to activate.

In September, Meridian received a warning letter from the FDA, saying the company failed to thoroughly investigate product failures, including EpiPen products, associated with patient deaths and severe illnesses. It said Meridian failed to take corrective actions until FDA’s inspection.

At the time Mylan said it did not anticipate any impact on EpiPen supply based on the warning letter.

EpiPen autoinjectors deliver a dose of epinephrine in the event of severe allergic reaction, such as to bee stings or exposure to peanuts.