Two of Uber’s top investors, Shervin Pishevar and Steve Russell, are threatening to sue three board members—including former CEO Travis Kalanick—if they vote in favor of a pending proposal that would remove “supervoting” powers on the company’s board of directors.

Such rights give some investors the ability to have multiple votes per share. The proposal, if enacted, would create equal voting rights, amid other changes, according to the Wall Street Journal.

“If you vote in favor of Tuesday’s proposal, our clients have authorized us to pursue any and all legal recourse including but not limited to actions against you personally,” the investors said in the letter.

Pishevar had previously asked Benchmark, an investment firm, to end its lawsuit against Kalanick, who no longer has a position with the company but still wields an outsized influence. Two days ago, Kalanick exercised his right to name two new board members, a move that will surely anger Benchmark, among others.

The letter was sent by Mark Geragos, a well-known attorney in Los Angeles. One of his colleagues, Ben Meiselas, provided Ars a copy of the letter.