US President Donald Trump paid $38m (£31m) in tax on more than $150m (£123m) income in 2005, a leaked tax return reveals.
Two pages of the tax return were revealed by US TV network MSNBC, triggering an angry response from the White House.
It said publishing the tax return was illegal.
Mr Trump refused to release his tax returns during the election campaign, breaking with a long-held tradition.
The two pages were a fraction of the complete return and did not include details of Mr Trump's income.
Correspondents say the leak is still significant because so little is known about President Trump's tax returns and the new information will increase pressure on him to release more.
Although leaking federal tax returns is a criminal offence, MSNBC host Rachel Maddow argued that it was exercising its First Amendment right to publish information in the public interest.
Journalist David Cay Johnston, interviewed on MSNBC, said he had received the documents in the post from an anonymous source.
In a statement issued before the broadcast, the White House said: "You know you are desperate for ratings when you are willing to violate the law to push a story about two pages of tax returns from over a decade ago."
It said Mr Trump had a responsibility to pay no more tax than was legally required.