Berkshire Hathaway, Buffett’s holding company, owns NetJets. NetJets is a company millionaires use in order to arrange fractional ownership of private jets — time shares, of sorts. NetJets lobbied like crazy, as Ryan Grim and Ariel Edwards-Levy at Huffington Post explained last month, to change the treatment under the tax code of flights on fractionally owned jets.

It’s complicated, but basically it’s about whether to charge a per-passenger tax as Washington charges commercial flights or a per-gallon tax as Washington charges the operators of private jets that are owned by one party. The latter treatment results in lower taxes.

Congress — mostly Ohio Republicans Pat Tiberi and Rob Portman, according to media accounts — stuck the NetJets provision into the transportation bill. The result is a “a much-reduced tax liability” for NetJets customers, and thus much higher profits for Warren Buffett. And earlier this month, the IRS began implementing this tax-law change.