In an open letter to Prime Minister Zoran Milanovic, Ribic responded to his comments in a TV interview on Thursday on unions' announcement of mass protests.
Ribic said the MHS would talk with union members in public services and that if they wanted it, "we will also organise demands for early elections because it is our democratic right to do so."
He described Milanovic's criticisms of all unions and himself as "unusually harsh" and that he had opted for this open letter because the PM communicated with the unions only through the media.
Ribic said that in the TV interview Milanovic accused the unions of preparing chaos and a coup, and described as "dangerous" Milanovic's claim that someone in the country had to be normal and sensible.
He invited Milanovic to an open dialogue on the difficult economic and social situation which he said was likely turn into a political crisis.
Ribic said the unions did not protest only against a three per cent wage cut in the public sector, but also because the PM had "torn down" the basic principles and international standards of social rights as well as collective agreements and institutions of social dialogue.
"You have not taxed the astronomic earnings, you are leaving the social inequalities that you inherited, seeing to it that you don't run afoul of the centres of power in the country," Ribic said in the letter.