Four senators are asking the FDA to help address the growing questions surrounding antibiotic use in farm animals.

In October, FRONTLINE’s The Trouble With Antibiotics examined the question of whether widespread use of antibiotics in farm animals is contributing to the rise of drug-resistant superbugs in humans. More than 20,000 people die from such infections each year, and up to 2 million get sick from them.

Up to 70 percent of antibiotics sold in the United States are used in agriculture. Farms use antibiotics in animals to protect them from disease. Many historically have also used the drugs for a practice known as “growth promotion” — helping the animals grow faster on less feed.

In December 2013, the FDA asked drug makers to phase out the use of antibiotics for growth promotion. But as FRONTLINE reported, no one is required to keep track of exactly how many antibiotics are given to animals.

On Tuesday, Democratic Sens. Dianne Feinstein of California, Tom Harkin of Iowa, Kirsten Gillibrand of New York and Elizabeth Warren of Massachusetts urged the FDA to issue a rule to increase data collection on the use of medically important antibiotics in agriculture. They also asked the group to work with veterinarians and the industry to develop a plan for collecting data on antibiotics use on farms.

Improved data collection would help the FDA determine the effectiveness of policies to encourage judicious antibiotic use, such as President Obama’s National Strategy for Combatting Antibiotic-Resistant Bacteria, they said.

“Data on antibiotic use and resistance enables federal agencies to take action to protect the public health and supports research into better understanding complex questions related to the development of antibiotic resistance and potential links to human health,” the senators wrote.  Furthermore, data regarding the distribution of medically important antibiotics is needed to monitor the impact of your new policies aimed at eliminating the injudicious use of these drugs in agriculture.”

Concerns about antibiotics on farms go back to at least the 1970s.

The Trouble With Antibiotics recounted how the FDA asked late in that decade for farms to begin restricting two antibiotics, penicillin and tetracycline, for fear that overusing them could fuel antibiotics resistance and threaten the health of humans.

But farm lobbies and industry groups attacked the proposal and said it would be financially ruinous. Additionally, one FDA official told allies, the business groups’ best ally in Congress successfully pressured the agency to back off the proposal by threatening to cut the FDA’s funding.

Watch The Trouble With Antibiotics below: