Spain's governing Socialist Party on Monday accused the Catholic Church of campaigning for the conservative opposition after bishops slammed laws on divorce and abortion at a mass rally in Madrid.

"I had the impression that it was a PP (Popular Party) rally run by cardinals," the Socialist Party's secretary Jose Blanco told local radio.

"Some of the things I heard were intolerable. They were making things up, like saying that human rights were going backwards in Spain," said Blanco, who described himself as a Christian.

Bishops at Sunday's mass rally said the traditional family was in danger due to laws passed since the Socialists won office in 2004 which have made divorce easier and reduced the Church's influence over education.

They also attacked abortion, whose legal status has not changed but which has been in the news in recent weeks following police raids on clinics illegally terminating pregnancies.

Estimates for attendance at the demonstration, addressed by Pope Benedict via video link, ran from tens of thousands according to left-of-centre media up to two million according to organisers.

The Socialists have a lead over the conservative Popular Party opposition of about two percentage points ahead of general elections set for March 9.

The Church has denied that Sunday's demonstration was in favour of any political party. Spain has become noticeably less Catholic since the death of dictator General Francisco Franco in 1975 and the return of democracy, with church attendance falling and attitudes to sex and marriage becoming much more liberal.