The acceleration of data center companies in the public equities markets is hitting the brakes.

Multiple firms tied to the artificial intelligence data center boom are delaying planned initial public offerings, The New York Times reports. The delays come as Wall Street weighs new obstacles facing data center development and uncertainty following pledges by leading executives to pump the brakes on the newest AI models.

In just the past week, data center developer SB Energy and power infrastructure firms Holtec and Aggreko have all reportedly slowed or paused plans to pursue IPOs, reflecting potential turbulence as close to a dozen other firms aim to go public in the months ahead, the Times reported.

Growing investor skepticism over the massive valuations being sought by some of these companies has prompted executives at at least three firms to rethink their plans to raise billions of dollars through public listings.

SB Energy — a SoftBank-backed developer of the largest planned U.S. data center campus — had planned to go public later this month, but that offering has now been delayed as investors reportedly balk at the firm’s proposed valuation north of $50B. Bankers are struggling to find enough buyers at the firm’s target share price, the Times reported.

While SB Energy has backing from AI giants like Nvidia, the reported hesitation may reflect the firm’s lack of a track record of bringing projects to fruition. The company says it has 8.8 gigawatts of capacity contracted or under construction, but nearly all of that is tied to a massive data center campus leased by OpenAI on federal land. It has yet to bring a single data center online.

Aggreko, which supplies small-scale power for live events and dining but had looked to go public in anticipation of fast growth from the data center sector, is also slowing down an IPO process because of the multiple challenges facing the data center sector, the Times reports.

Last week, nuclear energy firm Holtec — a firm with a growth plan centered around providing power for AI data centers — announced it is indefinitely postponing a planned IPO. The company had been expected to begin trading on the Nasdaq at a valuation of up to $10B but said in a statement that it was delaying the offering because of a number of factors that have “impaired investor confidence in the market for new public offerings.” At the top of the list of reasons cited by the firm was “uncertainty of data center development.”

This uncertainty is partially due to opposition to large-scale data center development that continues to rise. Lawmakers in states across the U.S. are proposing, and in some cases successfully enacting, measures that could make it much harder for data center developers to move projects forward.

These new development hurdles come as the industry is already facing a number of constraints that have caused the supply of data centers to trail far behind demand. Large blocks of power at the scale major tenants require have become practically nonexistent, while labor shortages have also stymied the pace of new data center construction.

Additionally, following a string of security incidents involving frontier AI models and a wave of viral warnings about their dangers, the leaders of several major AI labs have pledged restraint when it comes to pushing ahead with the newest AI models. AI stocks sank across global markets last week as fears spread that a slowdown could choke off the demand driving the industry’s spending boom.

Still, many across the data center industry say they are not worried about any slowdown in data center demand. And there is no sign that firms in the wave of data center IPOs expected in the coming months are changing their plans.

Over the last year, nearly a dozen data center companies have gone public, have filed for an initial public offering or have been reported to be exploring one. Claude-maker Anthropic, a huge occupier of data center space, is reportedly still on target to go public late this year. Infrastructure development firms exploring IPOs include CyrusOne, Vantage, Switch and Nscale.