Finland's largest financial services group OP Financial Group faces a reduction in its CET1 ratio after the ECB instructed it to increase the risk-weighting on its retail-related assets for a period of 18 months.

The decision comes after the ECB found shortcomings in the Internal Ratings Based Approach, or IRBA, process that OP Financial used to measure its capital adequacy and common equity Tier 1 ratio, especially that of delayed validations, OP Financial said in a statement Feb. 2.

The changes to its risk-weighting will reduce the Finnish company's CET1 ratio by less than 2 percentage points. Despite this, it expects to achieve its target of 22% capital adequacy by 2019-end.

OP Financial adopted the IRBA method under the supervision of the Finnish Financial Supervisory Authority between 2008 and 2011. Supervision of the group was passed to the ECB in November 2014.