Katherine Legge is planning legal action following the announcement that she will be replaced at Dragon Racing by Sebastian Saavedra for the 2013 IndyCar season.
The Briton, who returned to single-seaters with Dragon last season after three-year stint in the DTM, said in a statement that she signed a two-year sponsorship deal with TrueCar that she then took to Dragon for the 2012 season.
TrueCar has been named as the backer of Saavedra's entry for this year, which Legge believes is in violation of her deal.
"I am extremely disappointed that Dragon Racing and sponsor TrueCar have announced a replacement driver for the #6 car," Legge said.
"I received a letter from Dragon Racing terminating my services on January 18. My legal team had asked for details regarding the reasoning for this termination but none have been provided.
"I signed a two year deal for 2012/2013 with TrueCar as a sponsor, and then I took that sponsorship to Dragon Racing shortly thereafter.
"[Dragon Racing team owner] Jay Penske told [TrueCar CEO] Scott Painter that he would bring the Penske Dealerships onboard with TrueCar if I signed with Dragon Racing, so it seemed like it would be a good fit for all.
"I firmly believe that Dragon Racing and TrueCar cannot proceed without me and I will be taking legal action to protect my rights."
Legge started last season as part of a two-car line-up with Sebastien Bourdais, but was restricted to running the oval races after the team was forced to scale down to a single car following its mid-year split with engine supplier Lotus.
She made a total of 10 starts for Dragon with a best result of ninth at the Fontana finale, and says that she had been hoping to use that as the basis for a more stable 2013 season.
"It was a very difficult season last year, we did very little testing and I was made to sit out of some of the races," she said.
"I was very much looking forward to 2013, using the experience I gained last year as a springboard for greater success.
"I have spent most of this off-season trying to help TrueCar mitigate their costs and bring sponsors onboard with their [Women Empowered] Initiative, having invested a great deal of my own time, effort and money, so this has come as a huge shock.
"I am working feverishly to put something together. However having this happen so late in the game has made it virtually impossible."