underhand
adjective
UK uk/ˌʌndəˈhænd/ us(US also underhanded)done secretly, and sometimes dishonestly, in order to achieve an advantage:
This is an underhand attempt to resume commercial whaling.
Insurers have been accused of using underhand tactics to reduce the amount of compensation paid to homeowners who have been missold a mortgage endowment policy.
underhanded methods/tactics