Treasury Secretary Steven Mnuchin confirms that the tax plan the Trump administration will outline Wednesday afternoon will call for a 15 percent corporate rate.

At an event hosted by The Hill, Mnuchin — who declined to go into many specifics about the proposal — contended it would be "the biggest tax cut and the largest tax reform in the history of our country." The Treasury secretary did not set a specific goal for when he wants a tax bill to pass, but said "we want to move as fast as we can."

He said the White House wants a "combined plan" with the House and Senate, which could potentially clash with the administration over some provisions.

"I think it's clear that the House, the Senate and the administration are all on the same page," Mnuchin said.

Mnuchin and White House chief economic advisor Gary Cohn are expected to go into more detail about the plan — which appears to largely resemble President Donald Trump's campaign pledge — at a briefing later in the day. Mnuchin had set a goal of passing the first tax reform since 1986 by August, but the White House has recently backed off that deadline, signaling it wants to pass a plan by the end of the year.

Tax reform can prove an arduous process in which lawmakers have to balance the concerns of various stakeholders.

When Trump floated a 15 percent corporate tax rate as a candidate, analyses of the proposal estimated that it could add atrillions to the national debt. It is unclear what the current proposal would do to raise revenue to offset those major cuts, and Mnuchin declined to say Wednesday how specifically the administration would pay for the 15 percent rate.

The White House appears not to support one possible revenue-raising tool, the controversial border adjustment provision included in the House tax plan.

"We don't think it works in its current form, and we're going to continue to have discussions with them about revisions," Mnuchin said.

House Speaker Paul Ryan saw a preview of the plan and said the House is in "80 percent agreement," according to Reuters.

Mnuchin also did not answer whether the plan would hold to his previous comment that "there will be no absolute tax cut for the upper class." Speaking to CNBC in November, Mnuchin said any tax cuts for the wealthy "will be offset by less deductions."

Here are other potential aspects sought by Trump, according to reports: