Yes, al-isthighaathah from the dead ones or from the absent ones is shirk akbar, which takes the one who performs it out of the religion of Islaam – according to His Statement, subhaanaahu:
And whoever invokes besides Allah any other ilaah (object of worship) for which he has no proof, then his reckoning is with his Lord. Indeed the kaafiroon (disbelievers) will not be successful.
Surah al Mu’minoon (23) ayah 117
And His Statement, azza wa jall:
Such is Allaah, your Lord; His is the Kingdom. And those whom you call upon besides Him do not own even a Qitmir (the membrane over the date stone). If you call upon them, they do not hear your call; and even if they were to hear, they could not grant it to you. And on the Day of Judgement, they will reject your shirk. And none can inform you like the Khabeer (the One who is the All Knower).
Surah Al Faatir (35) ayah 13 and 14
And with Allaah is the tawfeeq. And may peace and blessings be upon our Prophet, Muhammad and upon his family and Companions.