The same-sex marriage bill proposed by the Spanish government is gaining momentum as it has cleared another legal hurdle on Tuesday - the Senate panel. On the brink of the full Senate reading next week where it is expected to be approved, the archbishop of Madrid and other senior bishops from the Roman Catholic Church will join a massive demonstration on Saturday 18th June protesting against the bill, Church officials have announced.

Saturday's rally in Madrid has been organised by a lay Catholic pro-family group called the Spanish Forum for the Family. Manuel Bru, a spokesman for Cardinal Antonio Maria Rouco Varela, the Archbishop of Madrid, said to the Associated Press, at least 15 bishops would join the march.

In his Sunday address, Antonio María Rouco Varela Cardinal Archbishop of Madrid said, "Matrimony and the family are realities rooted in the very nature of mankind and they cannot therefore be modified, inverted according to personal discretion or manipulated by human powers."

"If it is the state itself that establishes a law which ignores the essence of marriage, then the damage it causes to the true family, to children and society as a whole will be incalculable," the Archbishop of Madrid was quoted by the Guardian newspaper.

Half a million Catholics and members of the conservative opposition People's party are expected to be part of the march as well. The Guardian reported that more than 200 buses and half a dozen aircraft have been hired to ferry demonstrators to the Spanish capital from around the country.

"We Christians should speak now. We must go out on to the street," said Cardinal Ricard María Carles, archbishop of Barcelona.

Spain’s same-sex marriage bill has already passed the lower house of parliament in April. The senate version now has a conservative-backed amendment that allows civil officials who object to "gay marriage" to refuse to perform the ceremonies. Once it is passed in the Senate, homosexual marriage is expected to be legalised in Spain this summer.

Prime Minister Jose Luis Rodriguez Zapatero's Socialist’s government drafted the bill last year as one of the liberal agendas alongside with proposals to loosen divorce laws, and the abortion law among others. Zapatero’s liberal administration has raised tension with the powerful Roman Catholic Church.

Currently, Belgium and the Netherlands are the only countries in the world with legalised "gay marriage". Apart from Spain, Canada has enjoyed on-going success of same-sex marriage bill C-38 through the hurdle in the Parliament this week. With both Spain and Canada joining the list this summer, the number of countries that recognise civil unions are likely to double very soon.

Upon the strong historical action taken by Spain's Catholic Church against the social policies, Catholic communities from Europe and as far as Korea, Pakistan and Mongolia have sent their statements of support.

The bishops of Korea said in an official statement, "We fully support the courageous efforts of the Spanish Bishops’ Conference to protect life and the family. We wish to tell the Bishops of Spain: we the Church in Korea are with you as you strive to defend moral and social values in your country. May the Lord be with you and may your valuable commitment lead to good results."

From Lahore, Pakistan, Archbishop Lawrence Saldanha said, "The Catholic Bishops’ Conference of Pakistan guarantees clear and total support to the rightful moral position in favour of the family and life taken by the Catholic Bishops of Spain and hopes that the 18th June demonstration will be successful. We are in full spiritual communion with the Church in Spain in this most important campaign to protect the fundamental values of life and the family."

Numerous cultural and professional organisations in Spain are supporting the demonstrations including, Federación Española de Religiosos de la Enseñanza (FERE-CECA), Confederación Española de Centros de Enseñanza (CECE), Educación y Gestión (EyG), Confederación de Madres y Padres de Alumnos (COFAPA), Asociación Profesional de Profesores de Religión en Centros estatales (APPRECE); Confederación de Estudiantes (CES) and the Coalición Democrática de Estudiantes (CODE).