GOP mega-donor Charles Koch and his wife donated about $500,000 to Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE’s (R-Wis.) joint fundraising committee, just days after the GOP tax plan was passed.

Charles Koch made the donation 13 days after the plan was passed, which lowers the corporate tax rate and cuts estate taxes, the International Business Times reported.

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He and his wife also gave $237,000 each to the National Republican Congressional Committee on the same day, according to the report.

Charles Koch and his brother David Koch were both major advocates for the tax plan, pouring millions of dollars into efforts to get the legislation passed.

The pair is also planning on spending millions more on a public relations campaign for the plan, according to The Wall Street Journal.

Politico reported last year that Ryan isn't planning on running for another term, but Ryan has denied the report.

--This report was updated on Jan. 22 at 6:45 a.m.