Police discovered shortcomings in one in four taxis pulled over for inspection on Friday in the capital, the Finnish News agency reported on Saturday.
Failure to record rides was the most common infraction among the 94 vehicles inspected. Twenty-three drivers had insufficient logbooks, or no logbooks at all.
Logbooks are necessary for ensuring that drivers do not drive excessive hours and that working time bonuses are correctly paid.
The same shortcomings continue to persist in taxi operations, despite previous inspections drawing attention to the very same issues, the Helsinki Police said in a statement.
However, from a traffic safety perspective, the police noted that things were mostly in order.
The sting was carried out by the police in cooperation with the Transport and Communications Agency (Traficom), the tax office and regional state administrative agencies.