The two parties say in a joint leaflet which appeared in central and north Bosnia that the census is one of the most important processes for Croats and that it is mandatory.
Party activists have started distributing the leaflets around Bosnia. HDZ activists will distribute them in Croatia as well to highlight for displaced Bosnian Croats the importance of taking part in the census in their prewar homes.
"This is the only way to prove that we are here and that this is the region to which we are attached and whose citizens we are, and that what is ours is ours," the leaflets say. They urge Croats to declare themselves as such, their faith as Catholic and their language as Croatian.
Bosnia organised the last population census in 1991, when it had about 4.3 million inhabitants, of whom 780,000 were Croats. The Catholic Church in Bosnia estimates that the current Croat population is 440,000.