Out of a total of 35 persons who are suspected of 31 acts of corruption, five have been detained, according to the Ljubljana Police Department.
The house searches are being conducted by 100 officers in the Ljubljana, Koper and Kranj police districts.
While the police did not name any bank, Slovenia's largest bank, NLB, has confirmed that searches were conducted at its offices.
Several months ago, the bank reported to the police a suspicion of corruptive practices that had harmed NLB and some other banks in Slovenia.
"Today's searches are the result of our report. NLB is cooperating with the police in order to guarantee a successful end of the investigation, which is also in the interest of the bank," NLB said.
The police have so far established that several suspects, having worked together, secured loans for clients who were not credit worthy.
The crime ring has illegally gained EUR 850,000, according to the police, which said the investigation into the case had been launched last year.
The business newspaper Finance reported earlier in the day, quoting an official source, the racket had secured loans of up to EUR 15,000 in exchange for a commission.
Bank employees falsified their documents, with the clients taking out several loans with different banks on the same day in some cases.
Unofficially, the searches have also been conducted at the offices of the Slovenian branch of Unicredit and Sparkasse as well as at Lon and Delavska Hranilnica.
Abanka and Addiko Bank said their offices had not been searched, while Sparkasse refused to comment on the report.