Trump has repeatedly said that only the media cares about his taxes. More than 180 protests were planned across 48 states on Saturday - including in Montana.
"We have a tradition in this country of seeing what the interests - the business interests, the financial interests - of the person leading the free world (are)", Kinzinger said.
"We are under the same audit that existed, so nothing has changed", he said.
The demonstrations were timed to coincide with "Tax Day", April 15, which is traditionally the deadline for taxpayers to submit their annual returns to the U.S. Internal Revenue Service (IRS).
Democratic Representative Maxine Waters, of California, said there's nothing to prevent Trump from releasing his income taxes and that "the simple truth is he's got a lot to hide". What would his tax returns say about his belief in personal civic responsibility and a fair economy?
Thousands of voters from all over the country marched on Saturday to show President Donald Trump that they do indeed care about his tax returns. A new ABC/Washington Postpoll found that as many as 75 percent of Americans want Trump to release his taxes for public inspection. But there was also a protest near Mar-a-Lago, the private club where the president is spending this Easter weekend.
In another, he suggested that someone "should look into who paid for the small organised rallies yesterday", adding: "The election is over!"
UNIDENTIFIED CROWD: (Chanting) Donald Trump has got to go.
In blasting the protesters, Trump tweeted that "I did what was nearly an impossible thing to do for a Republican easily won the Electoral College!"
Trump said in an interview with ABC's George Stephanopoulos that he was considering releasing his tax returns.
When responding to a question at a newspaper editors' conference in Florida in 1973, Nixon replied: "I welcome this kind of examination, because people have got to know whether or not their president is a crook".