The posters in support of the An‘Nour mosque were seen around town on Tuesday but promptly removed by Winterthur authorities, who said they had not been pre-informed of the posters, reported news agencies on Wednesday.
Associations and communities are allowed to use free publicity sites around the town but must inform the authorities and have their posters checked beforehand, they said.
According to the newspaper Neue Zurcher Zeitung, the posters called for donations aiming at saving a mosque and referenced a bank account belonging to An‘Nour.
The mosque in question is an increasingly controversial presence in Winterthur.
It is currently suspended by the Zurich Federation of Islamic Organizations (Vioz) after its imam and three others were arrested in a police raid at the beginning of November.
The raid followed a tip off about a sermon given by the imam in late October in which he “called for the murder of Muslims who refuse to participate in communal prayer”.
Criminal proceedings have been opened against the imam and a member of the mosque's board for inciting crime and violence
The mosque reopened two days after the raid, but its future looks uncertain since the rental contract on the property is due to expire.
It's not the first time the mosque has hit the headlines.
In June police arrested a man with close ties to the mosque who was thought to be a key figure behind the radicalization of young Muslims in the area.
Winterthur is considered a hotspot for Islamic radicalization in Switzerland as at least five young men have left the city to join Islamic State in recent years.
The An'Nour has denied any connection to radicalization.