The company in late August had claimed that Kapoor "decided to move on" when it announced his exit.
However, Kapoor, in a damning two-page letter to the company Board, had said his "termination" was timed to deny him stock options (ESOPs).
In the letter dated July 27, Kapoor said the company had on July 10, 2015 informed him of "termination" of his employment with Micromax "on the malicious ground that I have presented for payment and got cleared bills for large amounts towards fuel expenses".
"I am entitled to ESOPS and other benefits. The valuation of the company has immensely increased due to my efforts. I have successfully got the commitment of huge investment in the company, the fruits of which the company has already started to reap," Kapoor said in the letter.
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Kapoor was the first chairman appointed last year by the company, which was founded in 2000.
Repeated attempts to reach Micromax failed to elicit any response while Kapoor said he had said whatever he wanted to say in the letter, copies of which had been submitted to the Ministry of Corporate Affairs (MCA).
"It is surprising that no notice was ever issued to me or any explanation was ever called from me and the entire process has been undertaken with the predetermined outcome to terminate my services for a concocted cause," he said.
Kapoor said no bills for fuel were even presented by him.
"The company had a direct arrangement with Janta Filling station and the bills were directly received by the company. By no stretch of imagination it can be stated that I have misappropriated any amount as no amounts were paid to me for fuel expenses. There were no cash transactions involved," the letter said.
"I have lost faith and confidence in the board...Needless to say that I would initiate legal action and make claims against the company," he added.
Among the papers filed with MoCA is also a July 6 letter from another director, Mohit Anand Bhatnagar resigning from the company "on instructions of SCI Growth Investments" which he represented on the Board.
Bhatnagar, a partner at Sequoia Capital, was a longtime investor in the company.