More than one in four members of the Civil Guard has contemplated suicide, according to interviews carried out by the force's biggest union, the AUCG.
Meanwhile, one in five have planned the act, while 4 percent have actually attempted to end their own lives.
In fact, 116 Civil Guard have killed themselves since 2005, official force statistics show.
All this comes despite the force having recently been voted the most respected public institution in Spain in a poll by the research institute CIS.
"It's our hidden tragedy," an AUCG spokesperson told Spain's 20 minutos newspaper in the wake of a new report into the problem.
"It's clear that we have to deal with the problem. People who speak to the CIS give the Civil Guard high marks but it's clear they don't know the conditions (the force) work under," the AUCG said.
The Civil Guard already have a team of psychologists working to prevent suicide, but the AUCG are now calling for a "transparent" monitoring programme "with investigative protocols for cases of suicide".
But the force says this already exists and all cases are investigated.
Daniel Jesús López Vega, who prepared the new AUCG report, interviewed over 1,000 agents and found that the military character and tough working conditions were taking their toll.
Twenty percent of officers said they had been bullied at work according to 2007 research. Meanwhile, officers clocked up over 17,000 days of mental health leave from 2005 to 2012.
Mental problems and personal issues also played a role, no less than in the general population, López Vega said.
But the ease of access to firearms was a major factor, the psychologist explained. More than 95 percent of Civil Guard suicides were with guns, he said.