If Mitch McConnell wants Democrats to help pass tax reform, the legislation can't include tax cuts for the top 1 percent of income earners or add to the federal deficit.

Those were the conditions laid out in a letter sent Tuesday from the bulk of Senate Democrats to President Trump and Senate Republicans.

"Tax reform cannot be a cover story for delivering tax cuts to the wealthiest," the senators wrote.

The Democrats also insisted that any tax package move through regular order, rather than through the special budgetary procedure known as reconciliation that would allow the GOP to bypass a Senate filibuster.

Democrats sent the letter as the administration eyes moving tax reform through Congress at an accelerated pace this fall.

Their terms would likely be difficult to meet. The tax reform plans Republicans favor are almost certain to result in tax cuts for the top 1 percent, because they include provisions like lowering the top income tax rate and ending the estate tax.

And McConnell has long said that reconciliation is the path forward for tax reform.

Nevertheless, White House legislative director Marc Short said Monday that he hoped Democrats would vote for tax reform, and called on activists to put pressure on Senate Democrats up for reelection in states that Trump won.

Three of those Democrats did not sign onto Tuesday's letter: Joe Donnelly of Indiana, Heidi Heitkamp of North Dakota and Joe Manchin of West Virginia.

To date, vulnerable Senate Democrats have faced relatively little need to go along with Trump's agenda. In the vote to confirm Neil Gorsuch to the Supreme Court, for example, only Donnelly, Heitkamp, and Manchin ultimately voted "yes."