The Tuscan cities of Pisa and Livorno lie only 15 miles apart, but they have been separated for centuries by a relationship of "cordial loathing," – hence the Livorno saying "Better a death in the house than a Pisan at the door."

Small wonder that sparks are flying after a government decreed that the proud provincial capitals would be merged to create a single province as part of a cost-cutting drive.

The decree, which was issued on Wednesday and deemed "irreversible" by one government minister, will reduce the number of Italian provinces, which sit below the country's regional authorities and above its municipal councils, from 86 to 31.

The move marks a climbdown from plans to scrap them all, but has inflamed ancient rivalries as cities fight over which will become the new provincial capital.

Nowhere have the clashes been more fierce than in Tuscany, where tension has simmered since the times of the Medicis. However, Pisa, Livorno, Lucca and Massa Carrara must settle their differences and merge by January.

Pisa, a powerful port in the 12th century, was eclipsed by the rise of Livorno – and the two cities have squabbled since.

A Livorno journalist, Mario Cardinali, told the Italian daily Corriere della Sera: "Pisans are proud of their glorious maritime republic and their university, but tend to be closed, calculating and egoistic."

Livorno was declared a free port in the late 1500s by Ferdinando I of Tuscany, and has attracted adventurers, people fleeing persecution in northern Europe and Jews forced out of Spain, said Cardinali, making residents more libertarian than Pisans. "We also remind Pisans that Livorno had administrative seniority over Pisa during the Napoleonic era," he said.

Natives of Lucca are not well disposed to Pisans either, since Pisa invaded Lucca in 1314, added Cardinali. "Until recently mothers in Lucca would scare their children by saying 'Let's go, the Pisans are coming.'"

The decree specifies that the largest town in a merged province becomes its capital – in this case Livorno – but a clause allows local politicians to strike deals, prompting fears of horsetrading.

The Lucca mayor, Alessandro Tambellini, suggested he might bid for his province to be the capital, with the backing of Massa Carrara. But, sensing the accolade could be snatched from Livorno, its mayor, Alessandro Cosimi warned that "people here are getting angry".

Rows have also erupted further inland in Tuscany, where the province of Prato will be merged with Florence and Pistoia. Roberto Cenni, the Prato president, has described the decree as "shameful" and held a press conference while sitting on a toilet in his office, claiming it was the only place worth discussing such a measure.

Local councillors in Prato followed up by parking a coffin outside the town hall and handing out leaflets denouncing "the death of Prato".

Before elections are held in the newly merged provinces in November 2013, the association of Italian provinces has pledged to overturn the decree and announced plans to protest on 8 November in Rome. Legal challenges are expected to follow.

"This government decision is the product of an authoritarian vision which damages local democracy," said the vice president, Antonio Saitta.