Madrid's Association of Atheists and Freethinkers (AMAL) is considering defying a local government ban by marching through the streets of central Madrid on Thursday, or Jueves Santo (Holy Thursday) as the day is known in Spain.
The group says this is not an atheist march but rather a demonstration against the economic privileges enjoyed by Spain's Catholic Church.
According to AMAL, they are protesting about a situation where the country´s Catholic Church continues to be subsidized to the tune of €11 billion a year despite massive cuts in education and health.
But Madrid's local government has banned the demonstration on security grounds, Spanish news agency EFE reported on Wednesday.
Madrid local MP Cristina Cifuentes said recently that the atheist march couldn't go ahead because it could cause "public disorder".
The politician also argued that AMAL's request to be allowed to hold a demonstration had arrived too late.
But AMAL chief Luis Vega said the government had got the dates wrong and that the fax sent by AMAL had arrived ten days before the march.
Cifuentes said the document had arrived on March 19th at 10am, or just hours before the fax arrived, reported La Gaceta newspaper.
Vega said, though, that his group's procession was definitely planned for Holy Thursday — on the day when "the Catholic Church invades our streets".
He also accused Cifuentes of prevarication and said there was "a tacit agreement between the courts and the police" when it came to the group's planned march.
"This is a very serious matter because the government´s decision has closed the door to any group that demonstrates during Easter Week," said Vega.
AMAL will decide on Thursday whether to go ahead with their march or not.
In 2005, a Eurobarometer study found that only 59 percent of Spaniards believed in God and 21 percent in a higher power.