Morocco's opposition Unified Socialist Party announced on Monday that it would boycott the 25 November parliamentary elections called by the king in response to pro-democracy protests.
The USP made the decision at an overnight meeting in Casablanca, joining two far-left parties in a boycott of the upcoming polls.
"They (elections) will not strengthen democracy in Morocco," Mehdi Lahlou, a member of the party's leadership, told AFP.
"This decision is in line with our position on the undemocratic practices witnessed during the constitutional referendum, such as the utilisation of mosques and brotherhoods close to the regime to promote the yes vote," he said.
Parliamentary elections were due to be held in 2012 but were brought forward following a 1 July referendum in which voters overwhelmingly approved a package of reforms limiting the powers of King Mohammed VI.
The referendum and early elections were an attempt by the 48-year-old leader of the Arab world's oldest monarchy to pre-empt protests inspired by the Arab Spring.
While some continue to argue that the new constitution shortchanged the people's democratic aspirations, the king remains popular and street protests have subsided.