Yushchenko on April 2 signed a decree to dissolve parliament and call early elections after accusing lawmakers close to Yanukovych of illegally poaching deputies from pro-presidential factions.
The prime minister and his allies have strongly opposed early elections.
Yushchenko earlier today ordered prosecutors and police to take action against any official who refuses to obey his decree.
The Constitutional Court on April 17 is due to begin hearings on the decree's legality.
Constitutional Court Takes Center Stage
As Ukraine's political standoff continues, attention has shifted to the Constitutional Court. Is it ready to resolve such a dangerous dispute? more
How Should Constitutional Courts Work?
RFE/RL spoke with Wojciech Sadurski, a professor at the legal department of the European University Institute in Florence. more