The first issue of the Ghad Party newspaper Al-Ghad (Tomorrow) was meant to go on sale on Wednesday, but the state publishing house al-Ahram refused to print it on Tuesday on the grounds that its papers were not in order, they said.
Wail Nawara, first assistant to detained party leader Ayman Nur, called it "another crackdown on civil liberties in Egypt".
"This shows how little the authorities can tolerate free speech and opposition and confirms the political nature of the accusations directed at Dr Ayman Nur," he said.
Nur faces charges of forging some of the affidavits which the party submitted last year in its application for recognition. The party and civil-rights organisations say the charges appear to be fabricated, while the United States has said the detention raised questions about democracy in Egypt.
Nawara said a party official had signed, under pressure and without authorisation from the party, a letter to the Supreme Press Council, which controls the Egyptian press, asking for the editor-in-chief to be changed.
"This shows how little the authorities can tolerate free speech and opposition and confirms the political nature of the accusations directed at Dr Ayman Nur"
Assistant to Ayman Nur
Changes in editors require the approval of the council, which is controlled by the ruling National Democratic Party.
Nur's wife and party colleague, Gamila Ismail, added: "The Supreme Press Council told us that we are missing some routine paperwork, which is not true."
Nawara said the authorities disapproved of Al-Ghad editor Ibrahim Issa because of his record for candour.
"The government wants to shut us up, and control all our actions because Ghad is not like other parties which simply obey every order they take," Nawara added.
In an separate freedom of expression case on Tuesday, the authorities set free without charge the third of three activists detained last month for distributing leaflets opposing
President Husni Mubarak, judicial sources said.