Two U.S. lawmakers are calling for action to rein in antibiotic use in livestock in response to a Reuters investigation showing how top U.S. poultry firms have been administering drugs to their flocks.

U.S. Sen. Kirsten Gillibrand, (D-NY), said she plans to introduce new legislation authorizing the Food and Drug Administration to collect data on “farm-level antibiotic use.” The pledge was part of a letter Gillibrand sent Tuesday to FDA Commissioner Margaret Hamburg. In the letter, Gillibrand said that “the scale of injudicious use” of antibiotics in poultry production documented by Reuters “was staggering.”

Another member of Congress, Rep. Louise Slaughter, (D-NY), introduced legislation in February 2013 that would require drug makers, livestock producers and the FDA to release more data on antibiotic use in food animals. On Monday, she urged fellow lawmakers to address the issue at a hearing on antibiotic resistance scheduled Friday before the House Energy and Commerce Committee’s subcommittee on health.

“Industry has kept data showing the rampant, dangerous use of antibiotics hidden from the public for one reason: to protect corporate profits at the expense of public health,” Slaughter said.

Reuters reviewed more than 320 internal documents, called “feed tickets,” that detail the practices of five major companies – Tyson Foods, Pilgrim’s Pride, Perdue Farms, George’s and Koch Foods. The feed tickets list the names and grams per ton of each “active drug ingredient” in feed. They also indicate the FDA-approved purpose of those medications, and specify during which stage in a chicken’s roughly six-week life the feed should be administered.

The documents show that antibiotics were given as standard practice over most of the life of the chickens, not just when the birds are sick. In every instance of antibiotic use identified, the doses were at the low levels that scientists say are especially conducive to the growth of so-called superbugs -- bacteria that can gain resistance to conventional medicines used to treat people. Some of the antibiotics belong to categories considered medically important to humans.

In interviews, another major producer, Foster Poultry Farms, acknowledged that it also has used the antibiotics chlortetracycline and penicillin selectively but not as part of standard feed. The two drugs are in the same classes as antibiotics considered medically important to humans by the FDA.

The FDA has issued voluntary guidelines to regulate antibiotic use by producers of poultry and other livestock. The use of antibiotics rated medically important by the FDA for growth promotion is scheduled to be phased out by December 2016. The FDA says it also inspects the mills where animal feed is made but does not examine the feed tickets themselves – documents that show how drugs are administered.

In response to the Reuters report, the National Chicken Council, an industry trade group, said that the majority of antibiotics approved for use in raising chickens are not used in human medicine, and pose no threat of creating resistance.

“We understand the concern about the use of antibiotics in farm animals and recognize our responsibility to ensure they are properly used for the right reasons to protect the health of animals, humans and the food supply,” said Ashley Peterson, the council’s vice president of scientific and regulatory affairs.

Gillibrand said the legislation she intends to sponsor would enable the FDA to track farm-level antibiotic use by collecting veterinary prescriptions. Under a new FDA rule, company veterinarians will be required to issue a prescription whenever antibiotics are used. But that rule doesn’t take effect until April 2016.

Some companies are reluctant to discuss how they medicate their flocks.

In a letter dated Sept. 8, Pilgrim’s Pride advised its growers to protect “our confidential and proprietary information (information such as the information contained on feed tickets for example).” Violating what the company called “biosecurity and confidentiality obligations” is “a terminable offense” and the growers could be liable for damages, the letter said. Growers were asked to sign and date the letter.

A Pilgrim’s Pride spokesman did not respond to a request for comment.