The group on Thursday said a public and private pressure campaign by Democrats and allies of President Joe Biden to discourage donations to No Labels and discourage potential candidates to run on the ticket goes beyond legally protected political speech.

"There is a group of activists, operatives and party officials who are participating in an alleged illegal conspiracy to use intimidation, harassment and fear against representatives of No Labels, its donors and its potential candidates," Dan Webb, a former U.S. attorney and current No Labels leader, said during a press conference in Washington.

No Labels, which has yet to name a candidate, has already raised more than $60 million and has qualified in 14 states, including Arizona, Nevada and North Carolina: states that are likely help decide the election.

No third-party candidate has won a modern U.S. presidential election, although some like Ross Perot in 1992 have played outsized roles as spoilers, taking votes from major party candidates. Democrats fear their party may splinter this time with a centrist third-party bid while Trump's loyal base sticks with him.

The eight-page letter from No Labels details a number of incidents that the group's leaders believe go beyond the routine bare-knuckle tactics of politics and could be potential crimes.

Holly Page, a No Labels co-founder, said she was threatened by a top Democratic official who told her: "You will never be able to work in Democratic politics again."

The official later added, "you are going to get it with both barrels," according to the letter.

No Labels identified Democratic-aligned groups like American Bridge, Third Way and MoveOn as part of the alleged conspiracy. American Bridge and MoveOn did not immediately return requests for comment and Third Way declined to comment.

The Justice Department did not immediately respond to requests for comment.

(Reporting By Jarrett Renshaw; Editing by Colleen Jenkins and Jonathan Oatis)

By Jarrett Renshaw