The two companies were given a joint fine of 38.8 million euros ($45.8 million) and Deutsche Telekom an additional 31-million-euro penalty by the European Commission in 2014.
The EU watchdog said the two had charged unfair wholesale prices in Slovakia to squeeze out broadband competitors in a practice known as margin squeeze that lasted more than five years starting from 2005.
Deutsche Telekom and Slovak Telekom subsequently challenged the decision at the General Court which in a 2018 ruling reduced Deutsche Telekom's fine by about a third to 19 million euros and trimmed the joint fine to 38.06 million.
The operators however decided to appeal to the Luxembourg-based Court of Justice of the European Union (CJEU) on points of law.
The CJEU threw out the appeals and kept the reduced fines for the companies.
The case is C-152/19 P Deutsche Telekom v Commision & C-165/19 P Slovak Telekom v Commission.
($1 = 0.8472 euros)
(Reporting by Foo Yun Chee; Editing by Emelia Sithole-Matarise)
By Foo Yun Chee