Tech companies are interested in nuclear power, but some utilities are blocking their progress.

Tech companies are increasingly looking to directly connect data centers to nuclear plants as they race to secure clean energy to power artificial intelligence, sparking resistance from some utilities over the potential impact on the electric grid.

Data centers, the computer warehouses that run the Internet, in some cases now require a gigawatt or more of power, comparable to the average capacity of a nuclear reactor in the U.S.

The data centers are essential to U.S. economic competitiveness and national security as the country competes with adversaries such as China for supremacy in the race to develop AI, said Joe Dominguez, the CEO of Constellation Energy, which operates the largest nuclear fleet in the U.S.

“When you’re talking about large [demand] load that also wants to use zero-emission energy, you’re going to bring it very close to nuclear power plants,” Dominguez said on Constellation’s second-quarter earnings call Tuesday. Constellation, headquartered in Baltimore, operates 21 of the 93 reactors in the U.S.

Constellation’s shares have surged 62% this year, the sixth-best stock in the S&P 500, as investors attach a higher value to the company’s nuclear power capacity to meet the growth in data centers. Shares of Vistra Corp., based outside Dallas and owner of six reactors, have doubled this year, the second-best performing stock in the S&P after AI chipmaker Nvidia.

Tech companies are building out data centers just as power supply is increasingly constrained due to the retirement of coal plants and as demand is climbing from the expansion of domestic manufacturing and the electrification of vehicles.

The largest grid operator in the U.S., PJM Interconnection, warned in late July that power supply and demand is tightening as construction of new generation lags demand. PJM covers 13 states primarily in the Mid-Atlantic region, including the world’s largest data center hub in northern Virginia.

Constellation’s Dominguez argued that connecting data centers directly to nuclear plants, called co-location by the industry, is the fastest and most cost-effective way to support the buildout of data centers, without burdening consumers with the costs of building new transmission lines.

“The notion that you could accumulate enough power somewhere on the grid to power a gigawatt data center is frankly laughable to me — that you could do that in anywhere that doesn’t start with decades of time,” Dominguez said. “This is an enormous amount of power to go out and try to concentrate.”

But co-locating data centers next to nuclear plants already faces controversy.

In March, Amazon Web Services bought a data center powered by the 41-year-old Susquehanna nuclear plant in Pennsylvania from Talen Energy for $650 million . But the agreement to directly sell power to the AWS data center from the nuclear plant already faces opposition from utilities American Electric Power and Exelon, who have filed complaints at the Federal Energy Regulatory Commission (FERC).

AEP and Exelon argue that the deal between Amazon and Talen sets a precedent that will result in less available power in the PJM grid area as resources “flee to serve load that uses and benefits from — but does not pay for — the transmission system”

“This will harm existing customers,” the utilities told FERC in a filing in June. Talen Energy has dismissed the objections as “demonstrably false,” accusing the utilities of stifling innovation.

“The rapid emergence of artificial intelligence and data centers has fundamentally changed the demand for power and leads to an inflection point for the power industry,” Talen said in a June statement. “Talen’s co-location arrangement with AWS brings one solution to this new demand, on a timeline that serves the customer quickly.”

FERC has requested more information on the service agreement between Talen and AWS. The regulator is holding a conference in the fall to discuss issues associated with connecting large electricity loads directly to power plants.

“It really is a great opportunity for there to be interaction between stakeholders and the commissioners in an informal setting like a conference, as opposed to doing so in litigation,” Kathleen Barrón, chief strategy officer at Constellation, said on the power company’s recent earnings call, referring to the fall FERC meeting.

Constellation and Vistra have backed the AWS-Talen agreement in filings to FERC, with each of their CEOs saying on their earnings calls this week that co-location and traditional grid connection will be needed to meet demand.

Barrón told CNBC that Constellation has “seen interest from many” tech companies in potentially co-locating a data center at one of its sites.

Vistra is having numerous conversations with customers about co-location and is “in due diligence for a number of sites,” CEO Jim Burke said Thursday. With the dispute in the PJM region over co-location, data center developers may take a closer look at Texas, which operates its own grid called ERCOT, Burke said.

“We’re seeing some interest in Comanche Peak,” Burke told analysts on the company’s second-quarter earnings call, referring to one of Vistra’s nuclear plants. Comanche Peak, about 50 miles outside Fort Worth, Texas, has two reactors with 2.4 gigawatts of capacity, enough to power 1.2 million homes in typical conditions and 480,000 homes in peak periods, according to Vistra.

And Dominion Energy has indicated it is open to connecting a data center to the Millstone nuclear plant in Connecticut. The Dominion service region includes northern Virginia, the epicenter of the data center boom.

“We continue to explore that option,” CEO Robert Blue said on Dominion’s second-quarter earnings call. “We do clearly realize any co-location option is going to have to make sense for us, our potential counterparty and stakeholders in Connecticut.”

Kelly Trice, president of Holtec International, a privately held nuclear company headquartered in Florida, said the U.S. needs to start thinking more about balancing the power needs of data centers with those of all consumers. Holtec is working to restart the Palisades nuclear plant in Michigan and has also had conversations with tech companies about nuclear energy.

“Essentially, the hyperscalers and the data centers can take all the power and the consumer not get any of that if we’re not careful,” Trice told CNBC. “So the balance there, where the consumers actually get what is rightfully theirs too, is a factor.”

“The United States hasn’t really started wrestling [with] that yet,” Trice said. “But I think we’re getting close.”