NASCAR has taken further steps to reduce Cup drivers' participation in its lower level Xfinity and Trucks series.
Stock car racing's governing body has made a series of rules adjustments in recent years to prevent its top tier drivers dominating the support categories too.
From next season drivers with more than three full-time seasons in the Cup series will be limited to five races each year in both Xfinity and Trucks. The current limit is seven.
In addition, any drivers earning points in the Cup series are barred from running in the regular-season finale and all playoff races in the other series as well as the two support championships' bonus money mini-series - Xfinity's 'Dash 4 Cash' races and the Truck Series' 'Triple Truck Challenge'.
NASCAR's senior director of racing operations Meghan Miley said the changes "continue our commitment to strengthening our race teams and providing a stronger field with even greater competition for our fans".
The existing limits had already had a dramatic impact on the Xfinity and Truck series.
Earlier in the decade, the majority of rounds of what is now Xfinity were won by full-time Cup drivers adding additional races to their programmes.
But this year only three of the 22 Xfinity races held so far have been won by a Cup regular, with Kyle Busch triumphing on each occasion.
Limiting Cup drivers' Xfinity participation was intended to underline its purpose as a feeder series developing talent for the top class.
The current Xfinity top three are all in their early 20s and affiliated with Cup teams - Richard Childress Racing protege Tyler Reddick currently leading Joe Gibbs Racing young gun Christopher Bell and Stewart-Haas's Cole Custer.
Kyle Busch is also the only Cup driver to have won in Trucks this year, winning five of the series' 17 rounds so far including a run of four in a row early in the season.