Most of those in line to benefit from the Trump tax cuts are not complaining. Plenty of business owners and investors cheered the changes as good for themselves and the economy.

But Mr. Prince has found camaraderie among an ad hoc group of wealthy individuals known as the Patriotic Millionaires. Founded in 2010 by Morris Pearl, a former BlackRock executive, the loose-knit group advocates higher taxes on businesses and the wealthy. In recent years, they have met with legislators in Washington and various state capitals, testified before Congress and endorsed candidates who endorse higher taxes on the rich.

“We’re very concerned about this huge inequality thing,” said Mr. Pearl. “And the tax cut was designed to make the rich richer.”

Now retired, Mr. Pearl is frustrated that his income from investments is not taxed at a higher rate. “I don’t work at all, but I’m making more money than most people who do work, and I’m paying less taxes than they do,” he said. “It’s a pretty good deal if you can get it, but it’s not good for the country.”

‘A Monstrosity’

This is not the first time millionaires have voiced their enthusiasm for higher taxation. In 2011, President Obama introduced the so-called Buffett rule. Named after the billionaire investor Warren Buffett, who has spoken out in favor of higher taxes for the rich, the tax would have applied a minimum rate of 30 percent on individuals earning more than $1 million a year.

In an op-ed in The Times, Mr. Buffett lamented that his tax rate was lower than any of the other 20 people in his office, and called for changes to the tax code that would ask more of him and less of middle-class wage earners. “My friends and I have been coddled long enough by a billionaire-friendly Congress,” Mr. Buffett wrote. “It’s time for our government to get serious about shared sacrifice.”

The Buffett rule was never enacted. And last year, Mr. Buffett, of all people, cheered the Trump tax cuts, calling them a “huge tailwind” for American companies.