Democratic leaders signed a letter demanding an un-redacted version of the Mueller report from Attorney General William Barr on Thursday.

Barr is expected to release a version of the report with classified information redacted for various reasons, but Democrats are demanding a full version.

"As a matter of law," the letter said, "Congress is entitled to the full report — without redactions — as well as the underlying evidence. We require that information in order to discharge our constitutional obligations: to develop and pass legislation and to conduct thorough oversight of the Executive Branch."

Among those signing the letter were House Speaker Nancy Pelosi (D-Calif.), Senate Minority Leader Chuck Schumer (D-N.Y.), Rep. Adam Schiff (D-Calif.), and Senator Dianne Feinstein (D-Calif.).

Democrats also addressed the reasons for the redactions, adding, "the Department of Justice has no legitimate reason for withholding these materials from Congress."

They have been voicing disappointment and anger with Barr over his comments that there was "spying" on the Trump campaign in the 2016 election.

"I am going to be reviewing both the genesis and the conduct of intelligence activities directed at the Trump campaign during 2016," he explained during testimony before Congress on Wednesday.

"I think spying on a political campaign is a big deal, it's a big deal," he added. "I think spying did occur."

Here's how Democrats responded to Barr's testimony:

Dem Senator: Barr Testimony On Breaking With Mueller 'Disturbing' | The Beat With Ari Melber | MSNBCwww.youtube.com