By Ross Kerber

April 24 (Reuters) - Median pay among top U.S. CEOs rose 7.5% to a record $16.8 million for 2024, a new study found, as big stock grants boosted leaders' reported earnings well beyond the pay received by U.S. workers.

The CEOs of Axon AXON.O and Union Pacific UNP.N were among those getting big pay boosts from stock awards, according to the review of pay among S&P 500 CEOs by ISS-Corporate, the corporate advisory arm of Institutional Shareholder Services.

Other CEOs also did well as their targets were set during the relatively stable days of 2023, said Roy Saliba, Managing Director at ISS-Corporate who oversaw the study. That was before U.S. President Donald Trump kicked off a trade war that has sparked turmoil in global markets in recent weeks.

"One thing that jumps out is that these numbers don't mesh with year-to-date stock performance or current company performance and the looming uncertainty. The time gap explains that, the pay decisions for 2024 would have been made at least a year ago," Saliba said.

He said his unit is advising companies to wait before changing plans to adjust pay to account for uncertainty in the markets. Boards could use a different set of performance measures that compare an executives' work against their peers, he said.

Saliba's study looked at 320 companies in the S&P 500 with pay data filed so far this year. The executives did relatively well; U.S. Bureau of Labor Statistics data shows average hourly earnings for U.S. workers rose 4% last year, while Commerce Department data shows inflation ran at just below 3% in 2024.

Company shares performed above those rates, helping drive the CEO's gains. Among the 320 companies Saliba reviewed the median total shareholder return was 15.1% in 2024.

At Axon, maker of the Taser stun gun, CEO Patrick Smith was at one extreme, officially receiving $164.5 million last year, up from $40,058 in 2023. In that year he received only a salary of $31,201 and $8,857 in other compensation including private air transportation.

The stock units that accounted for most of Smith 2024 pay are "an incentive for future performance in the form of a high-risk, high-reward compensation plan, and the value is realizable only if and when each set of stock price and operational goals are achieved," Axon's filing states.

Axon declined to comment.

At Union Pacific CEO James Vena was paid $17.6 million for 2024 versus $2 million for his service for part of 2023, after he was hired in August of that year. The majority of his pay last year reflects big stock and option awards that a spokesperson for the railroad said are performance-based.

"If the company does not perform well, his actual bonus and equity will reflect that and be less," said the spokesperson.

(Reporting by Ross KerberEditing by Shri Navaratnam)

((ross.kerber@thomsonreuters.com; (617) 412 0093;))