"Congress must get to the bottom of President Trump's recent allegation that President Obama wiretapped President Trump's phones during the 2016 election," wrote Graham and Whitehouse in a letter to FBI director James Comey and Acting Deputy Attorney General Dana Boente.
"We would be equally alarmed to learn that a court found enough evidence of criminal activity or contact with a foreign power to legally authorize a wiretap of President Trump, the Trump Campaign, or Trump Tower."
On Saturday, Trump fueled the wiretapping accusations with four tweets claiming that former President Barack Obama issued the alleged directive himself, an accusation Obama's team denies.
"Terrible! Just found out that Obama had my "wires tapped" in Trump Tower just before the victory. Nothing found. This is McCarthyism!" wrote Trump.
The president further questioned the legality of the action despite providing no evidence that it occurred. The White House has declined to provide evidence and declined to comment further pending a congressional investigation.
Graham and Whitehouse indicated that they would be "glad to review any such applications and orders once they are disclosed, and proceed as appropriate with the oversight the President has requested."