Washington (CNN) -- The Food and Drug Administration on Friday said it was studying a federal judge's order that it consider withdrawing two popular antibiotics from use in livestock.
In a ruling issued Thursday, U.S. Magistrate Judge Theodore Katz said that the FDA must issue notices to drug manufacturers that the drugs will be withdrawn unless the companies can prove they're safe. Katz didn't issue a full ban -- suggesting the manufacturers should be given a hearing to make their case.
The suit was originally brought by the Natural Resources Defense Council, which argued that the FDA has allowed livestock producers to use popular antibiotics penicillin and tetracycline in feed for more than 30 years for purposes other than treatment of illnesses.
The NRDC claims "the indiscriminate use of antibiotics in animal feed can lead to the growth and spread of drug-resistant bacteria capable of infecting people." Antibiotic resistant bacteria are fast-moving, can be deadly, and can infect otherwise healthy individuals.
In its statement, the FDA said, "We are studying the opinion and considering appropriate next steps."
Thursday's ruling can be traced back to decisions the FDA made more than 30 years ago. In 1977, the FDA announced plans to withdraw approval of some antibiotics used in livestock feed. The drugs have been used by livestock producers to help promote growth and feed efficiency.
At the time, the FDA found the practice of using antibiotics for non-medical reasons unsafe. Drug manufacturers requested hearings, but the FDA never scheduled meetings and nothing else was done. The approval remained in place.
In subsequent years, new medical evidence suggested that treating livestock with antibiotics increased risks to human health. But according to the judge's ruling, the FDA never changed its position.
In May, two petitions circulated urging the FDA to finish what it started in 1977. When the FDA didn't respond, the NRDC filed suit.
In December, the FDA withdrew the original 1977 notices saying they were outdated.
The suit alleged that the FDA's failure to withdraw approval of penicillin and tetracycline after the 1977 research was unlawful and violated the administrative procedure act.
According to the NRDC, 80% of antibiotics used in the United States is used in livestock. The group also says 29.8 million pounds of antibiotics were used in livestock in 2009, up dramatically from the previous decade.
Meanwhile, the ruling isn't sitting well with beef producers. The National Cattlemen's Beef Association noted its dissent in a statement saying its members were "disappointed with the decision," and that practices include the "judicious use of antibiotics to prevent, control and treat any cattle health issues."
If drug manufacturers fail to show that using the antibiotics in livestock is safe, the FDA commissioner must issue a withdrawal order. But the judge noted that if the drugs are deemed safe, the FDA cannot withdraw them from use.