BENGALURU (Reuters) – Shares of Interglobe Aviation Ltd fell as much as 19% on Wednesday after one of the co-founders of India’s largest airline IndiGo alleged violation of corporate governance rules at the parent group.

Interglobe shares hit their lowest since March and were on course for their worst day since January 2016.

IndiGo co-founder Rakesh Gangwal on Tuesday also asked the country’s securities regulator to intervene in the matter, a move that suggests that a previously reported row between Gangwal and fellow co-founder Rahul Bhatia was escalating.

“I have vigorously attempted for almost a year to persuade the company to shore up its governance standards, and all my attempts have been thwarted by the IGE Group,” Gangwal said in Tuesday’s letter to the Securities and Exchange Board of India, referring to Bhatia’s affiliate group.

Gangwal and Bhatia each own less than 40% in Interglobe, giving both co-founders a major say in its strategy and plans.