WASHINGTON (AP) — Most Senate Democrats and independents said Tuesday that upcoming legislation to rewrite the tax code should make sure the middle class doesn't pay more.

They won't support any upcoming GOP effort to overhaul the U.S. tax code that delivers tax cuts to "the top 1 percent" or adds to the government's $20 trillion debt.

That's the word in a letter signed by 45 of the 48 Senate Democratic caucus members. Republicans controlling Congress are gearing up to advance their tax measure this fall, promising to lower rates on businesses and individuals, while clearing out many tax breaks and deductions.

The letter says that Democrats hope to work with Republicans to promote investment and modernize the outdated tax code, but the terms laid out by Democrats are unlikely to tempt Republicans, who are planning to use a filibuster-proof Senate procedure to advance the legislation without their help.

"Any tax reform effort should not benefit the wealthiest individuals, who have already seen outsized benefits from recent economic gains," said the letter, authored by Minority Leader Chuck Schumer, D-N.Y., and others and provided to the media. "Tax reform cannot be a cover story for delivering tax cuts to the wealthiest."

The contours of the GOP tax plan are fuzzy at best, but House Speaker Paul Ryan, R-Wis., says he's not pressing for a large, deficit-financed tax measure. But keeping GOP promises for large rate cuts won't be easy under those conditions, given the difficulty in eliminating popular deductions and tax breaks.

The most recent successful tax reform effort was in 1986 and required a bipartisan push to overcome opposition from powerful interest groups.

GOP leaders also intend to reject another Democratic demand: advancing the measure under regular legislative procedures instead of through the planned fast-track path.

Three Democrats from states easily carried by President Donald Trump — Joe Manchin of West Virginia, Joe Donnelly of Indiana, and Heidi Heitkamp of North Dakota — did not sign the letter. Each of the three is up for re-election.

In Tuesday floor remarks, Schumer said that tax reform should focus on increasing "wages for working families, improving middle class job growth, promoting domestic investment while modernizing our outdated business and international tax system."

Added Schumer: "From what we've heard from the White House so far, their plan wouldn't do any of that."