The woman was working as an office secretary and according to prosecutors, she opened 48 postal mails addressed to prisoner patients.
According to the case, the letters never reached the prisoners but were found in the woman's possession.
The prosecutor is demanding a complete conditional prison sentence for an aggravated violation of communications secrecy and breach of duty.
The suspected incidents took place from November 2012 to August 2014.
The proceeding of the case began this week at the district court and will continue till June 6. The case will be discussed in closed session.
National broadcaster Yle previously disclosed the issue.