(49)Member States should be able to refuse or withdraw a credit institution's authorisation in the case of certain group structures considered inappropriate for carrying out banking activities, because such structures cannot be supervised effectively. In that respect the competent authorities should have the necessary powers to ensure the sound and prudent management of credit institutions. In order to secure a sustainable and diverse Union banking culture which primarily serves the interest of the citizens of the Union, small-scale banking activities, such as those of credit unions and cooperative banks, should be encouraged.