Thousands of Italians marched on Rome on Saturday to demand legal rights for unmarried same sex couples.

50,000 activists, including leftists from Prime Minister Romano Prodi’s coalition, took to a Roman piazza and rallied in support for a bill that would offer greater legal protection to unmarried couples.

Some demonstrators wore bishop’s mitres with slogans that attacked the Vatican.

Catholics in Prodi’s coalition government as well as opposition parties have promised to shoot down the bill.

They have drawn attention to an article in the constitution that recognises the family rights of “natural” unions “based on marriage.” They argue that the article only accommodates heterosexual unions.

In response to the rally, Catholic groups launched the “Committee for the Family.”

Olimpia Tarzia, the organisation’s president, accused the left of trying to “attack the family as an institution” and put gay unions on a par with marriage, according to Reuters

The Vatican has taken a similar stance.

In February Pope Benedict XVI said in a Vatican speech that the family “shows signs of ceding to lobbies capable of negatively eroding the legislative process.

“Divorce and free unions are on the rise, meanwhile adultery is viewed with an unjustifiable tolerance,” he added.

Pierferdinando Casini, an opposition member of the Christian Democrats’ Union, pointed to contradictions within the coalition and said that the “government has lost its way”.

But some gay rights groups have argued that the bill is not radical enough. Franco Grillini, a leader of the gay rights group Arcigay, pointed to legislation in other European countries.

“None of these countries has seen the apocalyptic forecasts about the fate of the traditional family come true,” he told Reuters.

“On the contrary, Denmark, the first country to introduce gay marriage, has a

higher birth rate than Italy,” he added.

The bill grew out of Prime Minister Roman Prodi’s 2006 election campaign and is currently being scrutinized by a parliamentary committee.

Vladimir Luxuria, a transgender leftist deputy and Prodi supporter told Reuters:

“We won the election by promising to do something for over a million Italians who are not linked by religious marriage but want their rights recognised.”

But he warned that because of Prodi’s tiny majority in the Senate, supporters of the bill had “to be sensitive and open up the debate to the centre-right opposition.”

Under the proposed legislation unmarried couples of any sexual orientation would be able to formally register with their local authority and receive legal rights in areas such as property, inheritance and employment.