The Conservative candidate for London mayor has been reported to the Crown Prosecution Service (CPS) over claims he "repeatedly attempted to mislead" voters with campaign leaflets.
Shaun Bailey used "City Hall"-branded paper to warn Londoners of an alleged 21.2% council tax increase.
The letter warned: "London mayoral council tax rise. Do not ignore."
The leaflet, sent in December, invited readers to sign a petition against any council tax rises.
While a footnote included Mr Bailey's name and the address for the Conservative Party headquarters, the Tory Party logo and name were absent from the letter.
The London Assembly member was reported to the CPS by Labour.
In its submission to the CPS, Labour called the leaflets a "fraudulent device", as described by the 1983 Representation of People Act.
Under election law, the CPS can investigate any breaches rather than the police.
'Work of fiction'
Labour deputy leader Angela Rayner called for the Tories to apologise.
She said Mr Bailey seemed "determined to insult voters' intelligence by bringing discredited Donald Trump-style fake news to London".
"He has consistently misled over TfL finances, the congestion charge and council tax, and his latest leaflets are literally a work of fiction," she added.
"Fake news, fake polls and fake leaflets will not only reflect badly on him and the Conservative Party but erode trust in politics."
This is a heartless, cheap trick to play at a time so many Londoners are worried sick about making ends meet. @shaunbaileyuk, you should apologise immediately for the distress your act of desperation will cause.— Luisa Porritt (@LuisaPorritt) December 14, 2020
This is inappropriate behaviour from someone standing for Mayor. pic.twitter.com/Z4tngAwB3g
Luisa Porritt, the Liberal Democrat mayoral candidate, posted a picture of the leaflet on social media on 14 December, labelling it a "cheap trick".
A spokesman for Mr Bailey said: "We published our leaflet because Londoners have a right to know when their mayor is planning to hike council tax."
The CPS confirmed it had received the letter from Labour's lawyers but said it would not be making any further comment.
The London mayoral election is due to be held on 6 May, having been postponed by 12 months due to coronavirus.