Can you provide hadith and Quran verses to support your answer. A lot of people say it is but I have only seen 1 verse in the Quran about it:
اتَّخَذُوا أَحْبَارَهُمْ وَرُهْبَانَهُمْ أَرْبَاباً مِنْ دُونِ اللَّهِ وَالْمَسِيحَ ابْنَ مَرْيَمَ وَمَا أُمِرُوا إِلاَّ لِيَعْبُدُوا إِلَهاً وَاحِداً لا إِلَهَ إِلاَّ هُوَ سُبْحَانَهُ عَمَّا يُشْرِكُونَ
“They (Jews & Christians) took their rabbis and monks to be their lords besides Allah (by obeying them in things they made lawful or unlawful according to their own desires without being ordered by Allah), and Messiah, son of Maryam, while they were commanded to worship none but One Ilah – La ilaha illa Huwa – Praise & glory be to Him from having the partners they associate (with Him).” (Quran 9:31)
But there's no direct ruling to Muslims saying that doing it would be shirk. What if you know the halal and Haram in Islam and follow it, but you see other Muslims do sin, and don't know/deny it's a sin and not tell them it's a sin. Is that considered shirk? What if you know the Muslims are stubborn and won't listen to you as well?