(Corrects proxy firm's name to Institutional Shareholder Services in paragraph 1)
March 8 (Reuters) - Proxy advisory firm Institutional Shareholder Services said on Thursday Tesla Inc shareholders should vote against a proposal for a $2.6 billion performance-based stock option grant for Chief Executive Officer Elon Musk.
Three days ago Glass Lewis said the same, claiming the proposed grant would dilute other investors and be too costly.
"While we recognize that Musk's leadership and his vision for Tesla in its mission to accelerate the world's transition to sustainable energy make him a unique CEO in many ways, the grant would ... dwarf those of top executives at the largest and most profitable public companies," ISS said.
Tesla, which reported its worst ever loss in the fourth quarter, is under pressure as its much-anticipated Model 3 sedan has already missed several key production targets.
Some analysts have questioned whether Musk's other interests, from space exploration to tunnel boring technology, are a distraction at what is seen as a critical time for Tesla.
Separately, Musk also took to Twitter on Thursday to call on U.S. President Donald Trump to challenge Chinese auto trade rules. (Reporting by Arjun Panchadar in Bengaluru; Editing by Shounak Dasgupta)