Napa is Truex's primary sponsor and in the first year of a three-year extension announced last August. The deal ran through the 2015 season and is believed to be worth at least $15 million a year.
"NAPA believes in fair play and does not condone actions such as those that led to the penalties assessed by NASCAR," NAPA said in a statement. "We remain supportive of the millions of NASCAR fans and will evaluate our future position in motorsports."
The company issued a harsh rebuke of MWR last week after NASCAR sanctioned the organization for its shenanigans in the Sept. 7 race at Richmond. MWR was punished for deliberately manipulating the outcome of the race in an attempt to get Truex into the 12-driver Chase for the Sprint Cup championship field.
NASCAR took the unprecedented step of kicking Truex out of the Chase in favor of Ryan Newman, who would have made it into the field instead of Truex without MWR's meddling. MWR was also fined $300,000, general manager Ty Norris was suspended indefinitely and all three crew chiefs for its drivers were placed on probation for the rest of the year.
The penalties levied against MWR led to a larger NASCAR investigation that uncovered at least one other case of race manipulation.
NASCAR chairman Brian France also ordered all competitors to give 100 percent at all times during a meeting in which it was made clear attempts to artificially alter the outcome of races would be prohibited.
Waltrip apologized for the first time for MWR's actions at Richmond.
"To the fans and those who made their voice heard through social media, as the owner, I am responsible for all actions of MWR," he said in a statement. "I sincerely apologize for the role our team played and for the lines NASCAR has ruled were crossed by our actions at Richmond. NASCAR met with the competitors in Chicago and we all know how we are expected to race."
Aaron's, sponsor of Brian Vickers for MWR, said it remains dedicated to the organization, but Clint Bowyer sponsor 5-Hour Energy said Thursday it was still evaluating its relationship with MWR.
NAPA's decision will end a relationship with Waltrip that dates to 2001. NAPA was sponsor for Waltrip for both of his Daytona 500-winning cars and moved with him when he formed Michael Waltrip Racing in 2007. The company took over sponsorship of Truex when he joined MWR in 2010 and as Waltrip's replacement.
This is the second scandal NAPA has been through with Waltrip, who was found to have a fuel additive in his engine in his debut race, the 2007 Daytona 500.
NASCAR docked the team 100 points, ejected crew chief David Hyder and executive Bobby Kennedy and fined Hyder $100,000 in one of the biggest cheating scandals ever at the Daytona 500. It was also Toyota's debut race. Waltrip had a miserable season that year, failing to qualify for 20 races with NAPA as his sponsor and nearly going bankrupt.
He recovered, in large part, after MWR co-owner Rob Kauffman pumped in much-needed cash and brought stability and accountability to the organization.
NAPA won four races with Waltrip, stayed on when Truex took over the car, and his victory this June at Sonoma was its first with him since he began driving the No. 56. Truex did qualify for the Chase with NAPA last season, finishing 11th in points, and was in contention for the final Chase wild card berth at Richmond while driving with a broken wrist.
Michael Waltrip Racing said in a statement it respects NAPA's decision.
"There is no doubt, the story of Michael Waltrip Racing begins with NAPA Auto Parts, but there are many more chapters yet to be written," the statement said. "MWR has the infrastructure and support of Toyota for three teams plus three Chase-caliber, race-winning drivers. With the support of our corporate partners we are preparing to field three teams in 2014. MWR is a resilient organization capable of winning races and competing for the championship and that remains our sole focus."
Waltrip also credited NAPA for his success as a driver and team owner.
"NAPA has been with me from winning two Daytona 500s, to missing races with a new start-up team, and back to Victory Lane again," he said. "The relationship grew far past that of just a sponsor, but more of a partner and a friend. We will not be racing a NAPA car in 2014, but I have friendships that will last a lifetime."
The loss of a primary sponsor, particularly with only nine races left in the season, is a big blow to Waltrip. It will be a tremendous challenge to quickly replace the money because NAPA is a rare sponsor that covers the entire 36-race Sprint Cup schedule.
Should MWR not secure sponsorship to replace NAPA, it could lead to layoffs of nearly 100 employees and the possible shuttering of Truex's team. Truex could be out of job, as well.
One solution could have been a partnership with Furniture Row Racing, which will lose its lone driver, Kurt Busch, after this season. Furniture Row tried during the summer to defect from Chevrolet to Toyota, only to learn Toyota didn't have the space to accommodate another team.
An alliance with MWR could have gotten Furniture Row in the Toyota family, and been a potential landing spot for Truex should Waltrip fail to figure out another solution to save his third car. But Furniture Row a week ago agreed to continue its arrangement with Chevrolet team Richard Childress Racing.
MWR also fields cars for Bowyer and Vickers, the two drivers who actively participated in the manipulations at Richmond to get Truex into the Chase. Bowyer spun with seven laps remaining to bring out a caution that prevented Newman from winning the race, and Vickers pitted late to benefit Truex.