Electric utility stock Constellation Energy (CEG -0.92%) tumbled 10% through 10:35 a.m. ET Monday morning despite beating analyst forecasts for third-quarter earnings this morning.

Wall Street anticipated Constellation would earn $2.64 per share, adjusted for one-time items, on sales of $5.7 billion. In fact, Constellation says it earned $2.74 per share, and sales exceeded $6.5 billion.

Constellation Energy Q3 sales and earnings

This good news gets better. Constellation's $2.74 profit was only a non-GAAP (adjusted) number. But earnings as calculated according to generally accepted accounting principles (GAAP) were $3.82 per share, an increase of 69% over last year's Q3 profit.

That's pretty impressive, considering Constellation's sales for the quarter grew only 7% year over year.

Of course, the big news in the quarter was Constellation's blockbuster announcement last month, that it will restart nuclear power Unit 1 at Three Mile Island, in order to supply electricity to Microsoft's artificial intelligence data centers over a 20-year term.

Problem is, that same power supply agreement seems to be weighing on Constellation Energy stock today.

Constellation Energy's bad news

As CNBC reports today, you see, the Federal Energy Regulatory Commission (FERC) has just rejected a request by another electric power utility, Talen Energy, to increase the amount of nuclear power it supplies to a data center operated by Amazon.

The FERC decision on Talen's Amazon project doesn't necessarily affect Constellation Energy's deal with Microsoft. Regardless, the two deals sound similar enough that Talen's bad news is bleeding over to affect Constellation Energy's stock price today, as investors make the inevitable comparisons.

No matter how small the risk that Constellation will see its own growth stymied by regulatory interference, the stock currently costs nearly 29 times forecast 2024 earnings of $8 to $8.40 per share. That's a high price to pay for a utility with only a 0.5% dividend yield and suddenly less certain growth prospects.

I wouldn't necessarily conclude that just because Constellation Energy stock is down today, this presents a great buying opportunity.