WASHINGTON — April 15, the traditional Day of Dread for taxpayers, is the backdrop Saturday for marches and rallies in Washington and nearly 150 other cities around the country aimed at pressuring President Trump to release his federal tax returns.

In Washington, a march from the Capitol to the Washington Monument, opposite the White House, will kick off with a rally on Capitol Hill featuring members of Congress.

Sen. Ron Wyden, D-Ore., and Reps. Maxine Waters, D-Calif., and Jamie Raskin, D-Md., are scheduled to speak in Washington. Rep. Jan Schakowsky, D-Ill., is speaking in Chicago. Rep. Ted Lieu, D-Calif., will speak in Los Angeles.

“What you saw beginning the day after the inauguration has not let up,” Schakowsky said. “We’re talking about intensity. The only question any of us get now is: What can I do?”

Rallies were also planned in nearly 150 cities, including New York, Boston, Sacramento, Calif., and San Francisco. Activists in West Palm Beach, Fla., will hold the “March a Lago” near the resort where Trump is spending the Easter weekend.

“We’re marching on Washington, D.C., and around the country to ask Donald Trump: WHAT ARE YOU HIDING?” the organizers say on their website. “We need a president who works for all Americans, and a tax system that does, too. Release your tax returns and commit to a fair tax system for the American people.”

Trump is the first U.S. president in modern history not to release his returns – every president since Richard Nixon has done so. Recent polling shows 74% of Americans want to see his tax returns.

“It’s about a lot more than just seeing somebody’s 1040s. It’s about whether or not the president of the United States is acting in the interest of the American people or whether he’s lining his own pockets or serving another master,” said Ezra Levin, executive director of Indivisible, among the major protest groups that's formed in the past few months.

“Congress has the power to find out and they’ve used it before," including on Nixon, said Levin, whose group is among the organizers.

The idea for the march grew out of the success of a women's march on Washington that drew millions of people. Jennifer Taub, who teaches law at Vermont Law School, got the ball rolling with a tweet calling for a #showusyourtaxes protest. Taub has testified before Congress and written a book about the 2008 financial crisis.

“I’m just a law professor who sent out a tweet,” said Taub, according to the Associated Press. “I’m psyched, and I think lots of people are psyched about this. We shall see.”

“I’m all about ‘follow the money,’” Taub said. “It tells us the story about people’s priorities.”

Through the march, the Democratic Party and progressives are attempting to reroute the grassroots energy that helped derail Trump’s bid to overhaul the Affordable Care Act toward their next goal: forcing a release of his tax returns and drawing the battle lines for the upcoming debate over U.S. tax reform.

More broadly, the coalition of almost 70 progressive groups is trying to take ownership of an issue — taxes — which Republicans have championed for the past 25 years, culminating in the formation of the conservative Tea Party.

In fact, Saturday is also the eighth anniversary of hundreds of Tax Day protests that marked the emergence of the Republican-aligned Tea Party. Although the Tea Party gathered steam around opposition to Obamacare, its roots are in a backlash to former President Obama's $787 billion stimulus program.

"It’s time to play offense on the tax issue," said Wyden, the top Democrat on the Senate Finance Committee. "The tax system in America is a broken dysfunctional mess. If you’re a cop or a nurse, it’s compulsory. It comes right out of your check," he said. "If you’re one of the fortunate few, you can do the Cayman Islands thing and decide what you’re going to pay and how you’re going to pay it," and often, pay not much at all, Wyden said in an interview previewing his remarks at the Saturday march.

In a Facebook page for the event, organizers said the march focuses on government transparency, conflicts of interest and an unfair tax system. They called on supporters to "show Donald Trump that he owes us transparency."

"Two-thirds of Americans are concerned that he may be putting his interests ahead of the country's," organizers said in a statement. "Until we see his tax returns, we can't know for sure."

As a candidate, Trump said he would not release his taxes while they were being audited. After the election, he said that only the news media cared about seeing the documents. "I won," he said.

Sean Spicer said Tuesday: “We filed our financial disclosure forms the other day in a way that allows everyone to understand.”

While April 15 is normally deemed Tax Day, this year it is Tuesday, April 18, because it falls on the weekend and there a holiday in Washington, D.C., on Monday.

Stanglin reported from McLean, Va. Contributing: The Associated Press