Political parties have been urged to suspend all door-to-door campaigning, including leafleting, during the current nationwide lockdown.
The Cabinet Office said doorstep campaigning was "neither essential nor necessary" and went against the spirit of the "stay at home" order in force.
The Lib Dems have defended activists who have continued to deliver leaflets ahead of May's local elections.
It said there were exemptions for voluntary organisations under the law.
But Labour says it has suspended volunteer leafleting and urged other parties to do the same.
As it stands, May's council and mayoral elections in England - including more than 100 contests delayed from last year - are scheduled to go ahead, although ministers have said the situation will be kept under constant review.
In a letter to representatives of political parties, Cabinet Office minister Chloe Smith said the government would be issuing guidance in due course about "appropriate conduct" in the run-up to the campaign and during it, including potential changes to the nominating process for the thousands of candidates due to take part.
But she said the government was very clear that face-to-face political activity at the moment was inconsistent with current regulations requiring people only to leave home where strictly necessary.
"The government's view is that these restrictions do not support door-to-door campaigning or leafleting by individual political party activists," she wrote.
"It is widely accepted that voters can continue to get campaigning information remotely.
"In order to reduce transmission of Covid-19 infections, door to door campaigning at this point in time is therefore not considered essential or necessary activity."
"I would ask that all parties follow this advice, and ensure that your supporters are aware of this position."
Speaking on Sunday, Lib Dem leader Sir Ed Davey said his party's volunteers were acting within the law and taking the same precautions as postal workers and delivery drivers when pushing leaflets through letterboxes.
"The guidance says there is an exemption for volunteer organisations, we've taken legal advice on that," he said.
"The advice we've given to all our councillors and volunteers is they need to wear a mask, they need to socially distance, they need to sanitise their hands."
Elections for the Scottish Parliament and the Senedd in Wales are also due to take place in May.