The Anti-Coup Alliance said on Monday that it is boycotting the referendum which is set to take place next month.
The alliance, also known as the National Coalition to Support Legitimacy, is made up of several parties and organisations including the Muslim Brotherhood.
Interim president Adly Mansour announced on Saturday that the referendum for the amended 2012 constitution will take place over two days, on 14 and 15 January.
The alliance made the announcement in a tweet, describing the constitution as the “coup constitution”.
The alliance claimed that there were European pressures “to participate and vote No” and that the alliance is rejecting these pressures.
The alliance’s rejection of the referendum comes after weeks of its continued protest to the unseating of former President Mohamed Morsi from power at the hands of the military. The alliance has been organising weekly protests to voice that rejection since Morsi’s ouster in July.
Constituent Assembly head Amr Moussa said on Sunday that the assembly is hoping for a 75% voter turnout in the upcoming referendum on the constitution while also calling on all divisions of Egyptian society to participate.
After months of convening to amend the 2012 constitution, Moussa handed the final amended version to Mansour on 3 December at the Presidential Palace.
Several parties have already announced their positions on the referendum, including Al-Dostour Party, which strongly supported protests that led to Morsi’s outser, called last week on Egyptians to “strongly participate” in the referendum. It also expressed its rejection of any campaign calling for boycotting the referendum.
Moderate Islamist party Misr Al Qawia Party also announced its position last week, urging Egyptians to vote No.
Islamist Al-Nour Party announced that they will vote Yes.