More than 400 American millionaires and billionaires have already answered the call: “Please join Responsible Wealth members and other wealthy individuals around the country in signing this letter to oppose the Republican tax plan.”

The letter has been signed by the likes of billionaire George Soros, Ben & Jerry’s founders Ben Cohen and Jerry Greenfield, and philanthropist Steven Rockefeller, according to the Washington Post, and will be sent to Congress this week.

“We urge you to oppose any legislation that further exacerbates inequality,” the letter states. “Tax reform should be, at a minimum, revenue neutral — without using gimmicks like dynamic scoring. We are deeply concerned that revenue loss would lead to deep cuts in critical services such as education, Medicare and Medicaid, and would hamper our nation’s ability to restore investments in our people and communities.”

Read: Tax plan to get rid of medical expense deduction.

The letter was penned by Responsible Wealth, a liberal organization that worked with Voices for Progress in an effort to rally the wealthiest 5% against President Donald Trump’s tax plan.

Bob Crandall, a former American Airlines AAL, -3.22% CEO, also signed on, the Post reported. “I think a tax cut is absurd,” he said. Republicans are “saying we can’t afford to spend money, but we can afford to give rich people a huge tax break.”

Specifically, Responsible Wealth slams Congress for trying to repeal the estate tax, which would only benefit those in line for a big inheritance.

“Repealing the estate tax alone would lose an estimated $269 billion over 10 years — more than we would spend on the Food and Drug Administration, Centers for Disease Control, and Environmental Protection Agency combined,” the letter stated.

The White House, for its part, says the bill is aimed at reinvigorating the U.S. economy, and the more money corporations have to spend, the more jobs and growth they can create. Or so the theory goes.

“Everything in our tax system is meant to encourage investment.” Gary Cohn, Trump’s chief economic advisor, told CNBC in an interview last week. And the words that likely resonated most with critics: “We see the whole trickle-down through the economy, and that’s good for the economy.”

Those signing the letter, however, don’t see it that way.

“We call on Congress to raise our taxes to bring in additional much-needed revenue and to restore investments to vital services,” it said. “Doing so will help create jobs, strengthen the middle class, and ensure America’s economic success.”