Rory McIlroy, Matthieu Pavon and Patrick Cantlay have been advised to get the USGA involved to investigate the shaft on Bryson DeChambeau's putter heading into the final round.
DeChambeau has been the standout player at Pinehurst this week so far, shooting seven-under-par through 54 holes.
He's the only player all week to shoot under par in each of the three rounds and holds a commanding lead heading into Sunday.
The American's power off the tee has been a huge part of his success so far as he's averaged over 317 yards in driving distance.
But his putter has also saved him on Pinehurst's treacherous greens as he ranks fifth throughout the US Open field in putting.
DeChambeau is unique in the sense that he's been playing with custom-printed clubs since April using 3D technology.
The irons were approved by the USGA just before the Masters earlier this year while he uses long-drive brand Krank for his woods.
He also uses a SIK Pro C-Series arm-lock putter and it's caught the attention of Grayson Murray's former caddie Kip Henley.
He took to X and posted a still of DeChambeau putting where he said the players fighting with the American at the top of the leaderboard should get the USGA to check the 30-year-old's putter.
“If I’m a player around the lead in the US Open I would ask the USGA to check the specs on this putter,” Henley wrote on X.
“The shaft has to lean away from [the] head at least 10 degrees.
"It sure looks vertical. Not being a d*** or hate him at all but it is a rule.”
Henley received plenty of backlash online for questioning the legality of DeChambeau's putter.
One message read: "Bad look on this tweet. Confident Bryson knows the rules."
Another replied: "This is a bad tweet. Like Bryson didn't check his equipment conforms to the rules when he dunks his golf balls in saltwater to make sure they are balanced."
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A third simply said: "That shaft is not vertical."
One other posted: "The heel is up no?"
Another wrote: "Lol I hope you're trolling."