Sounds like they are calling on US-based Islamist groups like CAIR to join them.

Via Ahram Online:

Egypt’s National Alliance to Support Legitimacy called for demonstrations on Tuesday at the United Nations (UN) headquarters to protest Foreign Minister Nabil Fahmy’s role as “representative of the state.”

Fahmy left Cairo for New York on Saturday, heading the Egyptian delegation that will participate in the UN’s 68th General Assembly, which starts on Tuesday.

“[The alliance] is calling the masses of liberty both inside and outside the country to a rally… as an expression of the Egyptian people’s rejection of the coup and whatever institutions resulted from it,” according to their statement on Sunday.

The alliance, an Islamist coalition established to challenge the ouster of former president Mohamed Morsi, which it describes as a “coup,” dubbed demonstrations: “The Coup does not represent Egypt.”

Since Morsi’s ouster the alliance has been staging anti-government demonstrations nationwide. However, turnout has decreased recently, with protesters more commonly taking to the streets within their own neighbourhoods.