Democratic senator Elizabeth Warren and Republican senator Josh Hawley are urging the US’s central energy information agency to provide better information on how much electricity data centers actually use.

In a joint letter sent to the Energy Information Administration Thursday morning, seen by WIRED, Hawley and Warren press the agency to publicly collect “comprehensive, annual energy-use disclosures” on data centers. This information, they write, is “essential for accurate grid planning and will support policymaking to prevent large companies from increasing electricity costs for American families.”

As the data center boom spreads across the country, there have been widespread worries from voters about how their massive energy needs may increase consumers’ electric bills; this concern helped shape some midterm elections in data-center-heavy states, including Virginia and Georgia. Last month, Hawley cosponsored a bill with Democratic senator Richard Blumenthal that would require data centers to supply their own power sources in order to protect consumers. Earlier this month, Donald Trump convened a group of executives from big tech companies at the White House to sign a nonbinding (and toothless) agreement pledging to pay for their own power for data centers.

“If we’re worried about ratepayers paying data-center energy costs, then knowing how much energy data centers are using is a necessary part of that calculation,” says Ari Peskoe, a director at Harvard Law School’s Environmental and Energy Law Program. “It’s not the only piece of information you need, but it certainly is a piece of the puzzle.”

There are lots of scary headlines floating around about how much energy data centers are expected to use over the next few years, but it’s surprisingly difficult to get official numbers from data centers on either their current or projected electric load. No federal government body collects numbers on energy use from data centers specifically. Information about water or electricity use at an individual data center can be considered proprietary business information, and is most often disclosed to the public voluntarily by the company itself. An increasing number of data centers are also turning to installing their own power separate from the grid—known as behind-the-meter power—making it even tougher to calculate total energy use.

Utilities are privy to information about energy use from data centers in their region; they use that information to forecast growth. But data centers will often shop around to different utilities, which, experts say, causes utilities to double-count projects and forecast “phantom” growth—data centers that will never be built in their region. The CEO of Vistra, a retail electricity company, said during its first quarter earnings call last year that utilities may be inflating electricity demand anywhere from three to five times beyond what is actually needed.

In December, EIA administrator Tristan Abbey said at a roundtable that he expects the EIA “is going to be an essential player in providing objective data and analysis to policymakers” with respect to data centers. The agency announced on Wednesday that it would be conducting a voluntary pilot program to collect energy consumption information from nearly 200 companies operating data centers in Texas, Washington, and Virginia, which will cover “energy sources, electricity consumption, site characteristics, server metrics, and cooling systems.”

While the senators praise the EIA pilot program, their letter includes several questions about how the agency plans to move forward with more data collection, such as whether or not the energy surveys will be mandatory and whether or not the EIA will collect information on behind-the-meter power. This information will be especially crucial, the senators say, to make sure that big tech companies that signed the agreement at the White House earlier this month pledging that consumers won’t bear the costs of data center electricity use will stick to their promises.