IndyCar title rivals Scott Dixon and Helio Castroneves will both take 10-place grid penalties for engine changes in this weekend's Fontana decider.
With the 500-mile superspeedway race placing tough demands on engines and recovering ground in the race likely to be straightforward given the ease of overtaking, tactical engine changes had been widely anticipated.
Ganassi driver Dixon leads Penske opponent Castroneves by 25 points going into the event.
While series regulations require a minimum mileage threshold of 2000 miles before an engine can be swapped, both Penske and Ganassi have elected to change the engines on their title-contending cars before that threshold was reached in order to minimise the risk of mechanical problems during the race.
In addition to breaching the rule regarding the minimum engine mileage, the change also means that both Dixon and Castroneves will be using their sixth new engine of the year.
Under the rules, each entry is only permitted five engines for the season, meaning that neither driver will be eligible to score points for their respective manufacturers.
Chevrolet and Honda go into the weekend tied on points.
Sarah Fisher Hartman's Josef Newgarden, AJ Foyt Enterprises' Takuma Sato, and Rahal Letterman Lanigan's Graham Rahal have also had new engines installed, taking them over the maximum allocation of five and meaning that all three will join Dixon and Castroneves in serving 10-place grid penalties, as well as being ineligible to score manufacturers' points.
With Ganassi's #10 entry (Alex Tagliani), the Dale Coyne Racing #18 car (Pippa Mann), and RLL's Jakes Jakes already having exceeded their five engine limit prior to this weekend, Honda now goes into Fontana trying to win the manufacturers' crown with seven of its cars ineligible for points.
Castroneves is currently the only ineligible Chevrolet-powered driver.
Dragon Racing's Sebastian Saavedra will meanwhile also be penalised 10 grid places for an unapproved change, although the Colombian remains eligible for manufacturer points as he is still within his five-engine limit.