The Muezzin is responsible for the Adhān, and the leader of the congregation is responsible for the Iqāmah
Authentic hadithعن علي رضي الله عنه مرفوعاً: «المؤذن أملك بالأذان، والإمام أملك بالإقامة».
‘Ali (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "The Muezzin is responsible for the Adhān, and the leader of the congregation is responsible for the Iqāmah."
Explanation
The noble Hadīth explains that the Muezzin is more entitled to determine the time of calling the Adhān, and that the Imām is more entitled to determine the time of calling the Iqāmah.
Source · Ibn Abi Shaybah - Al-Bayhaqi - ‘Abdur-Razzaaq
From the Hadith Encyclopedia (hadeethenc.com).