The leaflets recall that the parliament is obliged to call a referendum if 10 percent of the national electorate demands it.
Union leader Ozren Matijasevic said that the unions asked MPs to take into account the will of the citizens and decide to call the referendum.
The parliamentary committee on the Constitution and political system has recently decided to refer the matter to the Constitutional Court. The court is expected to consider the referendum question and whether there is any reason to hold the referendum after the government withdrew the draft amendments from the parliamentary procedure.