Proxy adviser Institutional Shareholder Services Inc. called Tesla Inc. [s" tsla] plan to award Chief Executive Elon Musk an estimated $2.6 billion compensation over a decade "unprecedented," and advised shareholders to vote against it. The award would be worth $260 million a year, leading to to "massive costs" over the years and it would dilutive for investors, ISS said in a note Thursday. "Even when annualized, Musk's pay opportunity would dwarf that of nearly every CEO at the largest and most profitable public companies. This raises even more questions given that Musk does not devote his fulltime attention to Tesla, and serves as the CEO of multiple other high-profile companies," ISS said. Competitor proxy adviser Glass Lewis came out against the proposal on Monday, also calling it too costly and too dilutive. Tesla unveiled the plan last month, and shareholders will vote on it later this month.