Democrat: We need Trump's tax returns to know how he'll benefit from his tax cuts

• Joe Crowley says he's glad President Trump released his tax proposal.
• Crowley adds that Trump should release his tax returns to let Americans know exactly how he'll benefit from the tax plan.

President Donald Trump should release his tax returns on good faith, a Democratic leader told CNBC on Thursday.

"I'm glad the president showed the courage to release his tax proposal. But not his taxes, unfortunately," said Rep. Joe Crowely, the House Democratic caucus chairman. "Because I think we need to know exactly how he will benefit from his proposal."

The New York congressman spoke on "Squawk Box" a day after the Trump administration released an outline of its tax plan. The White House said it would be the "biggest tax cut" in U.S. history.

Among other things, the plan would eliminate the inheritance tax and cut the top rate on "pass-through" businesses from 39.6 percent to 15 percent, which would benefit Trump personally.

Crowely called the tax proposal a "gaping loophole" for the wealthy.

At the briefing, Treasury Secretary Steve Mnuchin said Trump has no intention to release his tax returns, even though Trump previously said he would do so after an IRS audit was complete.

When White House spokesman Sean Spicer was asked last week if Trump would authorize the IRS to provide more details of the audit, the press secretary deflected. He said, "The president's view on this has been very clear" and "the American people understood it" when they elected him.

Earlier this month, tens of thousands of people had marched in more than 150 cities across the country to demand Trump release his tax returns. The White House has said Trump has released plenty of information.

—CNBC's Christine Wang contributed to this report.