One of the politicians behind the move told journalists on Tuesday the new group would stand on a joint political platform, but would steer clear of joining the present government.
Muhammad Sassi added he believed the north African kingdom was still "not going through a democratic transition".
"What we're experiencing is a time of gestation which has several possible outcomes... there's no political force in Morocco to provide a balance to the political power in place, which decides what it wants quite heedlessly."
The new grouping will include the Loyalty to Democracy party, the Unified Socialist Left, the Democratic Way, the Party of the Socialist Vanguard and the Itihadi National Congress.
Three of these movements – including Sassi's Loyalty to Democracy - are break-aways from the ruling Socialist Union of Popular Forces (USFP), the biggest party in the six-party coalition government.
The Democratic Way and the Unified Socialist Left were part of Morocco's Marxist movement in the 1970s.
In 1996, Moroccans approved by referendum a constitutional reform which made provisions for the creation of a bicameral system.
This allowed for a lower house elected for five years by universal suffrage and an upper house by indirect suffrage for nine years.