Spain was ranked 16th out of the 19 countries surveyed - with only Italy, Cyprus and Hungary faring worse - with an overall score of 21 percent for being able to safeguard against undue influence from lobbyists.
Still, as Transparency International and Professor Fernando Jiménez explained to The Local, all countries analyzed performed poorly in the report.
"It is a general problem across Europe and the difference between Spain and others, for example Germany at 23 percent, is not very big,” said Jiménez, a professor of political science at the University of Murcia and collaborator on the Transparency International research.
"In the case of Spain, there are more problems than it seems."
The report ranked 19 countries as well as three European institutions - the European Commission, the European Parliament and the Council of the European Union.
Only seven of the 19 countries surveyed had regulations to rein in lobbying’s impact - Austria, France, Ireland, Lithuania, Poland, Slovenia and the United Kingdom. Still, according to the report, most regulations are ineffective.
Together, the institutions and countries scored 31 percent when measured against international lobbying standards and best practices.
Slovenia scored the highest at 55 percent, followed by Lithuania at 50 percent and the United Kingdom at 44 percent.
The anti-corruption groups calls on EU institutions to adopt better lobbying regulations, such as establishing mandatory lobbyist registers where lobbyists must state who they represent, as well as publicly publishing a so-called “legislative footprint” that traces any outside input in legislation.
Jiménez said that in Spain, which has been hit hard by the global financial crisis, politicians have chosen to focus on economic changes rather than political ones.
"Corruption has not been a priority for governments," Jiménez told The Local. "In Spain, all of the focus has been on the economy. They don’t realize that an important part of a functioning country is a functioning political system, and that means addressing corruption."
Jiménez pointed to ongoing corruption investigations into members of the conservative Popular Party (PP), suspected of exchanging payments from business people for public contracts amounting to nearly €250 million.
Dozens have been implicated in the scandal so far, including high ranking members of the PP such as the former general secretary in Madrid Francisco Granados as well as the former party treasurer Luis Barcenas.
A country study of Spain in December by Transparency International wrote that with lobbying in the country, "it is almost impossible for the public to know who is influencing which decision-makers, by what means and with what effect."
A poll in February found that corruption was a bigger worry for Spaniards than terrorism.
Jiménez said that with newer parties like left-wing Podemos focusing their campaigns on fighting corruption, the topic could become prominent within debates ahead of the next general election at the end of the year..
"This is an opportunity for change because there are incentives and stimuli," he said. "But it will depend on the government’s capacity to improve and whether any reforms are in reality only aesthetic changes."