By Gavin Jones
ROME (Reuters) - Prime Minister Matteo Renzi's plans to reform Italian politics suffered a setback on Thursday when 13 senators from his center-left Democratic Party (PD) withdrew their backing in protest against his moves for constitutional change.
Renzi will not be assured of a majority in the Senate, the upper house of parliament, without the defectors, which will make it difficult for him to push through legislation.
The row centers on Renzi's plans to replace the Senate as an elected chamber with one made up of mayors, regional councillors and appointees of the head of state. He also plans to curb its powers so its approval is not needed to pass the budget or most other bills and he would remove its power to bring down a government with a confidence vote.
Renzi, the 39-year-old former mayor of Florence, set out his plans when he took office in February, saying the Senate was a drag on the legislative process and a financial drain on resources.
But the reform has been held up in the Senate Constitutional Affairs Committee. This week, Renzi removed two PD opponents of the plan from the committee.
In a shock response on Thursday, 13 PD senators said they were "suspending themselves" from the party and accused Renzi of authoritarian tactics at odds with the constitution.
Giuseppe Civati, a PD deputy frequently critical of Renzi, said his removal of the senators from the committee was "a political error" and rebuked him for trying to "eliminate dissent" in the party.
The senators did not say they would leave the PD itself and their action was seen more as a warning shot to Renzi than an immediate threat to his government's survival.
A crushing victory by the PD in elections to the European Parliament last month was widely seen as a personal triumph for Renzi, but despite his personal popularity he has so far made little headway with a raft of promised reforms.
When Renzi ousted party rival Enrico Letta to become prime minister he said he would "revolutionize" Italy with a major reform each month, but he has had to come to terms with the difficulties of leading a fractious coalition and resistance from sections of his own party.
He pushed through a popular cut in income tax for low earners, but promised reforms of the labor market, the public administration and the judicial system have been modest or have not yet been presented.
His blueprint for an overhaul of the electoral law, agreed in January with center-right leader Silvio Berlusconi, has also made no progress in parliament and Berlusconi frequently suggests he may pull his support.
Renzi, who has been on a tour of Asia this week, said on Wednesday the European elections showed Italians back him and he was determined to pursue reforms despite political resistance.
"Considering that votes count for more than vetoes, we will be carrying on with our heads high," he told reporters in China.
The rebels say they are in favor of reforming the Senate, including reducing the current number of 315 elected senators, but they want senators to continue to be elected directly rather than chosen by regional councils and mayors.
However, since winning the PD leadership, Renzi has proven highly effective in overcoming internal dissent and his supporters made clear they had no intention of compromising.
"Thirteen senators cannot be allowed to go against the will of 12 million voters and block the reforms that the Italians have asked for," said Cabinet Undersecretary Luca Lotti.
(additional reporting by Massimiliano Di Giorgio, writing by Gavin Jones; Editing by Janet Lawrence)