Sky Deutschland has warned UK licensees that anyone using its cards to screen Premier League football risks having them turned off without notice.
It follows similar warnings in June from Sky Italia, which is also owned by Rupert Murdoch's News Corporation.
The latest statement says: "Sky Deutschland has been informed that there are businesses in the UK selling Sky Deutschland viewing cards. This activity is not permitted by Sky Deutschland.
"If you have any information regarding the use or supply of Sky Deutschland viewing cards within premises in the UK then please email Sky Deutschland details of such to bar@sky.de.
"Sky Deutschland is stepping up activity in the UK to prevent use of our viewing cards at unauthorised addresses. Viewing cards will be terminated and Sky Deutschland will not refund any unauthorized dealers."
The statement says Sky Deutschland viewing cards "can only be registered within Germany, Austria, Switzerland or Luxembourg. Use of the cards outside these countries "is not permitted".
Ray Hoskin, boss of Media Protection Services, which investigates foreign satellite screenings on behalf of the Premier League, said licensees should not believe anyone who claims to be selling the cards legitimately.
"There are no UK agents for any of these viewing cards. They can be turned off at any moment — there are cards being turned off at the moment."
A statement from Sky Italia in June said it was aware of "unscrupulous dealers" selling Sky Italia cards to UK pubs "in contravention of the terms of use". The broadcaster warned it would "terminate viewing without warning".
The European Court of Justice is due to hear licensee Karen Murphy's appeal against her foreign satellite football conviction on 5 October.