The White House has lambasted Democrats for launching a “disgraceful” inquiry into alleged obstruction of justice and abuse of power by some of President Donald Trump’s closest allies.
A White House spokeswoman said the Democrats were “harassing” Mr Trump.
Earlier on Monday, the House Judiciary Committee had requested documents from 81 people and groups.
Among them were aides to President Trump and his campaign, members of his family, business associates and others.
House of Representatives Judiciary Committee Chairman Jerry Nadler, a Democrat, said it was the “obligation” of Congress to “provide a check on abuses of power” by the White House.
Mr Nadler, whose committee has the power to conduct impeachment hearings, also said it was “very clear” that the president had obstructed justice.
But Mr Nadler told ABC News it was too early to discuss removing the president from office.
President Trump dismissed Mr Nadler’s probe as a “political hoax”, but added: “I co-operate all the time with everybody.”
Democrats, who took control of the House of Representatives in January, have vowed to open investigations into the president and White House.
More than five House committees are now investigating alleged attempts by Russia to meddle in the 2016 election campaign, the president’s tax returns and potential conflicts of interest involving Mr Trump’s family.
Those inquiries are in addition to the investigation by Special Counsel Robert Mueller, who is expected to file his report soon.
What did the White House say?
In a statement, White House press secretary Sarah Sanders said: “Today, Chairman Nadler opened up a disgraceful and abusive investigation into tired, false allegations already investigated by the special counsel and committees in both chambers of Congress.
“Chairman Nadler and his fellow Democrats have embarked on this fishing expedition because they are terrified that their two-year false narrative of ‘Russia collusion’ is crumbling.
“Their intimidation and abuse of American citizens is shameful. Democrats are harassing the president to distract from their radical agenda of making America a socialist country, killing babies after they’re born, and pushing a ‘green new deal’ that would destroy jobs and bankrupt America.
“The American people deserve a Congress that works with the president to address serious issues like immigration, healthcare, and infrastructure.
Who received requests?
Trump Organization chief financial officer Allen Weisselberg, longtime Trump personal assistant Rhona Graff and ex-White House counsel Don McGahn are also on the list of names released by the House Judiciary Committee.
Donald Trump Jr has previously been forced by members of Congress to answer questions about a June 2016 meeting at Trump Tower, in which he sat down with a Kremlin-linked lawyer who had offered dirt on Mr Trump’s opponent Hillary Clinton.
Wikileaks, and its founder Julian Assange, have also been sent documents requests by the committee.
Wikileaks published emails stolen from the Democratic National Committee and released them during the 2016 campaign, causing political embarrassment to Mrs Clinton and her campaign team.
Roger Stone, Mr Trump’s confidant, who is currently under investigation by Special Counsel Robert Mueller for allegedly lying to prosecutors about his communications with Wikileaks during the presidential campaign, is also receiving a request from the committee.
After Mr Stone’s arrest in January, he denied that he played a role as an intermediary between the campaign and Wikileaks.
The documents would be used by the committee to determine which witnesses to call to testify in the coming months, a counsel for the House Judiciary Committee said.
If they do not comply with the next few weeks, subpoenas will be issued.
With his announcement, Mr Nadler is taking a shotgun approach to his investigations of the president, the BBC North America reporter Anthony Zurcher says.
He says the press release announcing the investigations doesn’t mention Russia or its election-meddling by name.
But the key components of the collusion allegations – the 2016 Trump Tower meeting, the WikiLeaks email dumps, changes to Ukraine policy in the Republican Party platform and the Trump-Russia business dealings – are all over the document requests.