Democratic presidential nominee Hillary Clinton is ready to turn up the heat on her Republican counterpart. She's expected to release her tax returns soon, something GOP nominee Donald Trump has refused to do despite it being a traditional expectation of presidential candidates.

Clinton is expected to release her returns in "the coming days, possibly as soon as Friday," according to ABC News, which cited "a source close" to the nominee. Clinton's running mate, Virginia Sen. Tim Kaine, "is expected to release his returns from the last 10 years," according to ABC.

CNBC also reported that Clinton will soon release her returns. The news outlet stated that her tax rate "reportedly is around 35 percent, while her charitable donations make up 10 percent."

The Clinton campaign has made it a point to remind the U.S. that Trump has not released his returns. After an audience member at a Clinton rally yelled out to "What about his tax returns," in May, the former secretary of state responded, "We’ll get to that."

"Because when you’re running for president and you become the nominee, that’s kind of expected," Clinton said. "So you’ve got to ask yourself, why doesn’t he want to release them? Yeah, well, we’re going to find out."

Every major-party candidate since 1976 has released their returns. Green Party candidate Jill Stein released her returns Thursday, asking Trump via Twitter, "Where are yours."

There are a number of reasons Trump might not want to released his returns, including, as the New Yorker points out, that he pays a low tax rate, or he donates very little to charity, or that the billionaire doesn't want tax professionals snooping around. Mitt Romney, 2012 Republican presidential candidate and an ardent anti-Trumper, suggested Trump was hiding a "bombshell" in his tax returns.

Trump, while still refusing to show voters his tax returns, has said that they are "all very beautiful."