Uber may buck this trend, though. The ride-sharing company is preparing to make its public market debut this year and is expected to do so with one class of stock.

Why should investors be wary of unequal voting rights?

As owners of a company, shareholders expect to have some sway over management. Full voting rights give them a greater voice in who’s on the board and how much executives get paid, and on big decisions, like whether to sell the company. Diminishing public holders’ voting rights can give insiders too much power and insulate executives who make poor decisions.

Strong boards, as well as the looming threat of activist investors, do a lot to assure top executives are responsive, says Glenn Kelman, chief executive of Redfin, an online real estate brokerage.

“The feeling that I serve at the pleasure of the board, that it is a privilege to work at Redfin, is fundamental to this company and the best of business culture,” he said.

It’s hard to say definitively whether companies with unequal voting rights perform better or worse over time. Google has grown strongly over the years, but so have Apple, Amazon and Microsoft, which don’t give special control to insiders. Viacom’s stock has done poorly while CBS’s has done quite well; Sumner M. Redstone , with the help of his daughter, Shari Redstone, controls both companies through voting shares.

Much also depends on the type of control a company grants. Robert J. Jackson Jr., a commissioner at the Securities and Exchange Commission, has cited analysis showing that companies that give control to insiders in perpetuity ended up with lower valuations on the stock market than those that planned to get rid of unequal voting rights after a certain period.

The question of control may become crucial when a company gets into trouble. Mark Zuckerberg, Facebook’s chief executive, faltered in his response to abuse of the company’s network and data. Shareholder advisory groups last year pressed for changes that they said would improve governance, including setting up a special risk committee on the board, but they did not get the necessary votes. Mr. Zuckerberg enjoys the protection of powerful voting shares. Facebook did not respond to a request for comment.