Early Christian inscriptions include appeals connected with Peter, Paul, and the martyrs, though individual dates and readings require caution. Origen speaks of angels and the souls of the righteous joining the Church’s prayers. By the fourth century, appeals to martyrs’ intercession are explicit in writers and homilies across East and West.
The objection was not invented at the Reformation. Vigilantius argued that the dead could no longer pray for the living. Jerome answered him directly in 406, appealing to the martyrs’ life in Christ and their continuing prayer (Against Vigilantius). That exchange is valuable precisely because it shows both the established practice and recorded dissent.
Orthodox Christians do not worship the saints. All prayer is answered by God, and Christ alone is mediator in the unique saving sense. Asking the glorified members of Christ’s body to pray is an extension of the communion of saints—not a rival altar beside Christ.
Primary source
Jerome, Against Vigilantius: https://www.newadvent.org/fathers/3010.htm