The warning, stemming from an April inspection by U.S. regulators, does not restrict production or product shipments from the plant in La Aurora de Heredia, Costa Rica, Hospira said on Tuesday in a regulatory filing with the U.S. Securities and Exchange Commission.

Among the issues cited by the FDA were ongoing problems with the company's Plum brand infusion pump, which Hospira recalled in February 2011 because of problems with its alarm. The company received complaints of alarm failures even after a supplier redesigned the part, the FDA said in the letter.

Hospira said it was still evaluating actions and associated costs to address the issues raised by the FDA.

"It seems FDA, with this warning letter, is not fully satisfied with their efforts to correct the alarm problems," Morningstar analyst Michael Waterhouse said.

An Hospira spokeswoman said the company was switching alarm components for the pump, a process it expects to complete by early 2013.

The maker of medical devices and injectable specialty drugs has been working for several years to resolve manufacturing issues at some of its plants.

Hospira, based in Lake Forest, Illinois, said in February that it had resumed production of injectable drugs at its Rocky Mount, North Carolina, plant, after a maintenance shutdown. Manufacturing problems at that plant had led to shortages of anesthesia and other drugs.

Earlier this month, Hospira's new Chief Executive Michael Ball told analysts the company was making progress addressing various manufacturing issues.

Hospira shares were up 1.3 percent after hours from a close Tuesday of $33.36 on the New York Stock Exchange.

(Reporting by Susan Kelly in Chicago and Bill Berkrot in New York; Editing by Gary Hill and Phil Berlowitz)

• A Permanent Economic Emergency