That it is; they are being investigated for violating section 371 of the Norwegian penal code, which reads:
Section 371.Fraud
A penalty of a fine or imprisonment for a term not exceeding two years shall be applied to any person who with intent to obtain an illicit gain for himself/herself or others
a) causes, strengthens or exploits a mistaken belief and thereby deceives someone into doing or omitting to do something by which someone suffers a loss or risks a loss, or
b) makes use of false or incomplete information, modifies data or a computer system, uses a credit or debit card which belongs to another person, or otherwise illicitly affects the result of automated data processing, thereby causing someone a loss or risk of loss.
Specifically, Tidal are accused of violating paragraph b) above.