An acrimonious dispute between leading shareholders of Indian low-cost carrier IndiGo has gone public, hammering the company's shares.

A 49-page document posted on India's BSE contains a letter dated 8 July 2019 from shareholder Rakesh Gangwal alleging governance improprieties, and previous correspondence from chairman Rahul Bhatia, in which he accuses Gangwal of using allegations over governance as a ploy to take greater control of the airline.

Gangwal and his affiliates, the RG Group, control 37% of the company, while Bhatia and his affiliates, the IGE Group, control 38%.

The news has pushed IndiGo shares down 19%, and comes seven weeks after the carrier vehemently denied media reports of a rift between the two men. The documents, however, suggests the dispute has been brewing at least since late 2018.

Gangwal's allegations, also issued to the National Stock Exchange, allege a disregard for governance, apparent efforts by IGE to control board and executive appointments, and state concerns about the use of related party transactions (RPTs).

The RG Group proposes to call an extraordinary general meeting (EGM) to address these issues, and for shareholders to pass a resolution for company managers and senior directors to strictly adhere to the company's code of conduct.

The document contains a previous letter from Gangwal, dated 12 June 2019, in which he defends the use of RPTs. He dismisses Gangwal's efforts as a naked attempt at gaining greater control and refuses a call for an EGM.

He accuses Gangwal of "purposely delaying ongoing negotiations with OEMs" for aircraft acquisitions, paving the way for IndiGo to set this up as an independent function.

The Securities and Exchange Board of India has asked for clarification in the matter.