Under a controversial law which came into effect on September 1st last year, illegal immigrants are denied treatment at public hospitals and health care centres in Spain unless they are under 18, pregnant, or in case of accidents.
"We ask lawmakers to be sensitive to the suffering this law is causing and take the necessary steps to return to the previous situation, when health care was guaranteed to all people who live in Spain," said Alvaro Gonzalez, head of Doctors of the World in Spain.
"From a rights perspective, it is unfair, from an economic perspective, it is ineffective, from the point of view of public health, it is dangerous," he added after meeting with lawmakers to discuss the impact of the law.
Many patients with chronic diseases like HIV and cancer who had lost their access to health care were abandoning treatment while people who had received organ transplants had stopped taking anti-rejection drugs, the aid group said in a report.
It has documented over 700 cases where health care services should still have been provided, such as in accidents or for pregnant women, but which were denied to people.
"These over 700 cases demonstrate the absolute chaos of the application of this law, with a significant deterioration in medical care," said Gonzalez.
Restricting access to health care to illegal immigrants would lead to an increase in spending in the medium term because it will cause the number of people needing emergency treatment to soar, he added.
Many of the 873,000 people who the government has recognized as having lost their access to health care because of the reform had lived legally in the country before they became unemployed and lost their work permits, the aid group said in its report.
"After all these years of contributing to the state budget they have lost one of the most basic rights, to health care," it said.
Prime Minister Mariano Rajoy's conservative government has vowed to find €150 billion ($195 billion) in savings between 2012 and 2014 through a painful austerity programme that has sparked mass demonstrations.