A £240,000 advertising blitz will be launched today by the Cabinet Office minister, Mo Mowlam, and Louise Casey, director of the Rough Sleepers Unit, which argues that pennies given to beggars may "go towards the fiver needed for the next heroin hit".
National newspaper and magazine adverts will call on the public to "change a life" by donating to homeless charities in the run-up to Christmas.
But in a forthright attack on the initiative, Britain's biggest homeless charity warned that it would send out the wrong message.
Chris Holmes, Shelter's director, said: "We agree that we must tackle the problems of begging and street culture. However, in this instance we feel unable to support the strategy, which we believe is misjudged.
"Some of the headlines already generated by this campaign risk over-simplifying the issues at the expense of vulnerable people on the street."
The charity warns that the government risks intensifying hostility to rough sleepers, who already live in a "very dangerous environment ... They are more likely to be attacked and abused."
Ms Casey, who was formerly deputy director of Shelter, is concerned that giving change to beggars fuels drug and drink addiction.
But Shelter warns that while there are gaps in services to treat homeless drug addicts, drinkers and the mentally ill, withdrawing money from beggars will simply leave a vulnerable group of people with no money and no escape route.
"If people are forced to find other ways to maintain a drugs habit, they may be forced into more serious crime, or working for drug dealers. Any messages which deter the public from giving to beggars, however subtle, will compound the existing stigmatisation."
In Brighton, which has a high concentration of rough sleepers, the local newspaper has conducted a campaign against beggars. The Evening Argus has been praised for its campaign by Ms Casey and by the Home Office minister, Lord Bassam.
The anti-begging campaign has come under fire from social policy academics, who protested to Tony Blair that it was "potentially harmful". Dons, including Ruth Lister of Loughborough University, warned it was likely to lead to an increase in crime and prostitution.
The latest government figure for the number of rough sleepers is 1,180. Shelter says this is likely to be an under-estimate.
Shelter is urging the government to draw up a task force bringing together voluntary agencies, the Rough Sleepers Unit, the Home Office, police, DSS, and psychiatric experts to develop long-term strategy.