A group of Berkshire Hathaway investors from the AFL-CIO wants to require the company to reveal Warren Buffett’s successor.

The labor union’s AFL-CIO Reserve Fund submitted a proposal that Berkshire shareholders will vote on at the annual meeting this May.

The proposal would address something many Berkshire shareholders have worried about for years because so much of the company’s success is generally attributed to the 81-year-old Buffett.

But the proposal faces an uphill battle because Berkshire’s board opposes it unanimously, and together that group controls 38 percent of the voting rights. Buffett himself controls about 34 percent of vote.

The board says it doesn’t see any benefit to publishing its succession plan. The board knows who would replace Buffett as CEO now if needed, but that could change over time.