Speaker of the House Jesús Posada recently described the move as a way of stopping anybody from causing “commotion” and “strengthening the Republican struggle”.
The 76-year-old king, hurt by royal scandals in the twilight of a reign that steered Spain from dictatorship to democracy, ceased to be covered by Spain's 1978 constitution when he handed over the throne to his son Felipe on Thursday.
Under Spanish law, the king "is inviolable and shall not be held accountable".
In October 2012, that immunity thwarted two legal suits demanding that Juan Carlos undergo paternity tests to show whether he was the father of two extramarital children.
According to Spanish online daily Público, the lawyer of Albert Solá, one of the alleged illegitimate sons of Juan Carlos, is looking to take advantage of the monarch’s current lack of immunity by presenting another plea for paternity tests on Monday before a Madrid court.
The same left-leaning newspaper wrote on Friday that Juan Carlos’s legal shield is being rushed through Parliament by adding it to a constitutional bill amendment focused primarily on labour conditions is the public sector.
There has been no suggestion that the king is linked to his daughter Cristina and her husband Iñaki Urdangarin's alleged money laundering but international news sources such as the New York Times and NBC have previously questioned how he managed to amass a fortune of over €2 billion.
An estimated 10,000 Spanish members of parliament, judges, prosecutors and members of the government are already afforded a legal privilege for actions taken as part of their official duties.
If approved in Parliament in the coming weeks, the legal immunity shield will also cover King Juan Carlos’s wife Queen Sofía, both of whom have been allowed to retain their royal titles.