Mr Maroni, a member of the federalist Northern League, told Italian television he had asked his party to decide by today whether he should stay at his post and called for the decree to be scrapped in its entirety, rather than amended.
'I am ready to resign my mandate on Monday,' Mr Maroni said.
His statement turned a political storm over the decree into a full-blown crisis for Mr Berlusconi's two-month-old coalition government, swept to power on a wave of public disgust with corruption in politics.
The League, which built its reputation on fighting graft, is the biggest party in parliament and ensures Mr Berlusconi's three-party coalition its majority.
Mr Maroni made his threat just hours after Mr Berlusconi said he was backing the decree to the hilt and would amend it only to make it harder for magistrates to hold suspects in preventive detention.
Rejecting talk of a whitewash for corrupt politicians as a 'despicable lie', the media tycoon said in a statement: 'I may be courting unpopularity but I will do everything in my power to empty the prisons of everyone held there against the universal principles of human rights.
'No citizen should be imprisoned without first being convicted. In Italy, in the Second Republic, justice must return to being a model of civility.'
In an interview with the daily L'Unita published yesterday, Mr Maroni had said a radical amendment of the decree might be acceptable. 'The decree must be rescinded or at least radically modified, but in the opposite manner to that proposed by Berlusconi,' he told the newspaper. 'Otherwise I would have to reconsider my remaining here in the Interior Ministry.'
Four leading members of Milan's elite pool of 'Clean Hands' magistrates spearheading the assault on graft told their superiors yesterday they were resigning their posts.
The move by the four, including the charismatic Antonio Di Pietro, made good a threat they made on Thursday to be asked to transfer to other work in protest at the decree.
The measure, which Mr Berlusconi says was approved unanimously by his cabinet, was issued on Wednesday and removes corruption, bribery and a string of other crimes from a list of offences for which suspects can be held in preventive detention in jail.
Mr Maroni said the published text differed from a draft he had approved and said he had received assurances that corruption suspects would not be freed from jail.
'I have decided to put my job in the hands of the federal council of the Northern League so that they can assess my behaviour to decide whether I had the wool pulled over my eyes or whether I have betrayed the years of battle the Northern League has waged against this system of corruption,' he said.
A government spokesman and cabinet-ranking member of Mr Berlusconi's Forza Italia party, Giuliano Ferrara, rejected Mr Maroni's allegations and accused him of infantile behaviour.
The decree remains in force for 60 days but will not take a permanent place on the statute books unless it is approved by parliament. The National Alliance, the third partner in the coalition, has also said it wants the decree changed.
Mr Ferrara said on Friday that Mr Berlusconi's government would 'pack its bags' if the measure failed to get through parliament.
Almost 500 people, including 53 corruption suspects, have already been released from Italy's overcrowded prisons, whose population has doubled to 53,000 in two years.
In Naples, protesters jeered 'Thief, Thief', spat and threw coins as the former health minister Francesco De Lorenzo, suspected of plundering funds on the backs of the sick, was released from the city's Poggioreale prison.
Mr De Lorenzo and the former Socialist party deputy leader Giulio Di Donato, who was held in the same jail, were both driven home in police cars with black plastic bags over their heads to be held under house arrest.
'I asked for guarantees that De Lorenzo and Co. would not be let out, and I got them,' Mr Maroni said.
He estimated that 20,000 to 30,000 inmates of Italy's jails, where half the prisoners are awaiting trial, could be freed under the decree, which he called a threat to public order. The Italian prison department estimates 4,000 could benefit.