The National Alliance to Support Legitimacy (NASL) said on Monday that the current interim government has "lost a new round" after a low turnout in overseas voting for the constitutional referendum.
The pro-Mohamed Morsi coalition, in a statement, called the low turnout of Egyptian voters abroad a "failure to the draft constitution."
The Elections Committee reported on Monday that only 15% of voters had turned out to cast their ballots. The percentage is a sharp decline from the 40 percent of expatriates who voted in the 2012 constitution referendum.
However, on Sunday, Deputy Foreign Minister Hamdy Loza attributed the low turnout of expatriate voters to the cancellation of an option in which ballots could be sent in by mail.
In a phone interview with Egyptian private satellite channel MBC Misr, Loza explained that in the 2012 constitutional referendum, voters had been able mail votes to their designated embassies and councils.
However, according to Loza, the Supreme Elections Council eliminated this option from the 2014 referendum to avoid legal challenges.
The scrapping of postal voting contributed to the fall, foreign ministry spokesperson Badr Abdel-Atti also told Ahram Online.
The number of those who voted in person this year (103,000) was higher than in the 2012 poll (92-93,000), Abdel-Atti noted.
In its statement, NASL reemphasized its message for Egyptians to boycott the elections, alleging that even a 'no' vote would be turned into a 'yes' by the current regime's "systematic rigging."
The alliance has also called for nationwide protests during voting on the referendum in Egypt on 14 and 15 January, but asked its followers to avoid protesting near polling places.
Egypt's interim head of state Adli Masnour had urged Egyptians to vote on the charter that represents "the first step to a civil modern democratic state."
Voting by expats is a recent addition to Egyptian politics, implemented after the January 2011 uprising.
Egyptians abroad were able to vote in this referendum from 8 to 12 January.
The newly amended constitution was drafted after the suspension of the one approved under former president Mohamed Morsi, following his ouster.
Its approval will complete the first step in the roadmap that envisages parliamentary elections and a presidential vote in mid-2014.