Tom Watson has written to broadcasters calling on them to "rise to the challenge of Boris Johnson's lies" during the General Election campaign.
The shadow culture secretary accused the Prime Minister of having a history of not telling the truth and urged TV and radio chiefs to be aware of this in their coverage of the countdown to the December 12 poll.
Mr Watson's letter to the BBC's director general and the chief executives of other major broadcasters refers to the "serious matter of honesty in public life and trust in politics".
The shadow culture secretary said: "Ensuring honesty in public life is a responsibility that we all share.
"Boris Johnson's wilful disregard for basic standards of decency are a threat to democracy.
"We appeal to the media to do what they do best and challenge Boris Johnson's repeated attempts to rely on fake news, lies and distortions.
"In previous campaigns, there was a reasonable expectation that politicians attempted to abide by relative standards of decency but in Boris Johnson we have a Conservative leader who wilfully ignores those standards.
"Boris Johnson's long history of lying and misleading people is well documented. Indeed, he has been fired twice for lying, and has lied about everything from his bike to the backstop, from tariffs on socks to the Supreme Court."
