The Eastern Churches

The Eastern churches objected that the Council of Ephesus, in 431 A.D., had forbidden adding to the Nicene Creed (in its Constantinople version), without a decision of another ecumenical council. 

[https://orthodoxwiki.org/Filioque]

Question: What was the objection of the Eastern churches to the addition of "filioque" to the Nicene Creed?