Portland’s executive-pay surcharge will be levied as a percentage of what a company owes on the city’s so-called business license tax, which has been in place since the 1970s. City officials estimated that the new tax would generate $2.5 million to $3.5 million a year for the city’s general fund, which pays for basic public services such as housing and police and firefighter salaries.

Criticism of how much chief executives are paid has risen in recent years as their compensation has grown substantially. In 2015, the median compensation for the 200 highest-paid executives at public companies in the United States was $19.3 million, up from $9.6 million five years earlier.

Comparing such compensation with how much lower-level employees earn is likely to show a very wide gulf. A 2014 study by Alyssa Davis and Lawrence Mishel at the Economic Policy Institute, a liberal-leaning advocacy group in Washington, found that chief executive pay compared with the earnings of average workers had surged from a multiple of 20 in 1965 to almost 300 in 2013.

Thomas Piketty, a professor at the Paris School of Economics and an authority on income inequality who wrote “Capital in the Twenty-First Century,” said he favored the Portland tax as a first step.

“This is certainly part of the solution,” Mr. Piketty wrote in an email, “but the tax surcharge needs to be large enough; the threshold ‘100 times’ should be substantially lowered.”