An IndyCar team owner -- whose driver won the Indy500 in 2011 -- claims he's being hosed by his biggest sponsor ... who bailed on a $2 million deal AFTER he covered his car in their logo.
The man behind the suit is Bryan Herta -- a former racer who owns the Bryan Herta Autosport racing team which competes in the Verizon IndyCar series.
Herta claims he struck a $2 million deal with the people behind Integrity Energy Drink back in April -- and immediately plastered the company logo all over the team's car ... complete with a fluorescent green paint job to match the Integrity colors.
But according to a lawsuit filed in L.A. County Superior Court and obtained by TMZ Sports, Integrity failed to live up to its name ... and only forked over $470k in payments.
Herta claims he went after company honchos for the money -- and got an email from the CEO apologizing for the payment problems ... but NEVER got the remaining $1.53 mil.
In the suit, Herta claims the lack of funding put his squad at a "severe competitive disadvantage" -- forcing the team to scale back important race prep to save money.
Herta is demanding the remaining $1.53 mil -- plus damages.
A lawyer for Integrity tells TMZ Sports ... "Any allegations made against my client should be viewed with high scrutiny. There is more to this situation than just a simple allegation. There exists evidence to counter any claim made by the claimant."