The foreign ministry, in a strongly worded statement, charged that she was "trying to thwart Morocco's decision to regain its natural and legitimate place within its pan-African institutional family".
Dlamini-Zuma had "delayed, in an unjustified manner, the circulation of Morocco's demand to other members" in September, it said in a statement.
She was "keeping up her obstruction by improvising a new procedural demand, previously unheard of and unfounded... to arbitrarily reject the letters of support from AU member states", it said, without giving details.
The ministry accused Dlamini-Zuma of acting "contrary to her obligation of neutrality, of AU rules and norms, and of the will of its member states".
Rabat officially requested to rejoin the AU in September, 32 years after quitting the bloc in protest at its decision to accept Western Sahara as a member.
Morocco has occupied the sparsely populated Western Sahara area since 1975 in a move that was not recognised by the international community.
It maintains that Western Sahara is an integral part of the kingdom even though local Sahrawi people have long campaigned for the right to self-determination.
In 1991, the United Nations brokered a ceasefire between Moroccan troops and Sahrawi rebels of the Algerian-backed Polisario Front but a promised referendum to settle the status of the desert territory is yet to materialise.
The Moroccan online website Le360 on Wednesday accused Dlamini-Zuma of "a blatant lack of neutrality" and taking orders from Algiers.