It has long been regarded as more of a national sport than a misdemeanour. And it has long benefited from the seemingly boundless indulgence of the Italian Roman Catholic church.

But now the head of the Italian bishops' conference, Cardinal Angelo Bagnasco, has unambiguously declared that "evading taxes is a sin". He called for "serious, effective and relentless" action against tax dodgers.

The cardinal's remarks are a boost to the technocratic government of Mario Monti, which is running a high-profile drive to root out evasion as it struggles to eliminate Italy's budget deficit and start paying back the country's €1.9tn (£1.6tn) public debt.

Among those often accused of avoidance, if not evasion, is the church itself. Its premises are exempt from property tax.

Critics have long maintained that the church takes unfair advantage of a 1982 law intended to benefit non-profitmaking organisations by claiming exemption for income-generating properties it owns, such as private clinics and guesthouses run by religious orders. This and other tax breaks enjoyed by the church have been the subject of an inquiry by the European commission.

Monti's predecessor, Silvio Berlusconi, keen to maintain the support of the church in the face of sex allegations levelled against his private life, was reluctant to act.

Bagnasco's comments prompted speculation of an agreement to pre-empt the threat of action by Brussels against the Italian government. Massimo Franco, a columnist for the daily Corriere della Sera, said: "The most likely hypothesis is that the cardinal's words put the seal of approval on an already drafted accord."

The head of the Italian bishops told his fellow prelates the church did not seek "improper self-exemption".