Senior government insiders say that Mr Blunkett, now a backbench MP, is furious at plans to reinstate the drug's original class B status less than two years after he moved it into the low-risk C category.
The Government is expected to make an announcement this week on the classification of the drug in the light of new research linking its use to mental illness. Charles Clarke, the Home Secretary, has already said that he will launch a public awareness campaign about the dangers of the drug because of widespread confusion.
It is understood that Mr Blunkett telephoned Mr Clarke last week to warn that tightening up the laws on cannabis would be a mistake. He also made his views known to the Prime Minister.
One senior figure said that there was a heated conversation between Mr Clarke and Mr Blunkett.
Cannabis was moved from class B to class C in February 2004 on the recommendation of the Advisory Council on the Misuse of Drugs, and lobbying from police, who said they needed to focus on class A drugs.