Pfizer Inc. said Tuesday it recalled one million birth control pills in the U.S. because the pills weren't made with enough contraceptive to prevent pregnancy.

Pfizer learned that the packets either contained too many active tablets or too few -- prompting the massive recall. The problem was caused by mechanical and visual inspection failures on the packaging line, according to The Associated Press.

As a result of this packaging error, the daily regimen for these oral contraceptives may be incorrect and could leave women without adequate contraception, and at risk for unintended pregnancy, said Pfizer, in a statement on the U.S. Food and Drug Administration Web site.

The recall impacts 14 lots of Lo/Oval-28 tablets and 14 lots of generic Norgestral and Ethinyl Estradiol tablets, Pfizer said. The drugs are manufactured by Pfizer and marketed in the U.S. by Akrimax Rx Products.

Pfizer said there are no safety risks with the drugs, but the recall was ordered since the risk in unintended pregnancy may rise.

The drugs have expiration dates of between July 13, 2013 and March 31, 2014, Pfizer said. They have been distributed throughout the U.S.