You can read the state of emergency proclamation (pdf) (hat tip: sassy lawyer). Back in May 2001 the President declared a "state of rebellion" when the pro-Estrada demonstrators got rowdy and marched on the Presidential palace. She got a lot of flak for that one, so this time it's called a "state of emergency."
I'll leave it to the lawyers to sort out the legalities. Two provision of the Constitution have been invoked:
1. Article 18 Section 7 - suppression of rebellion; ("state of rebellion", now studiously avoided);
2. Article 12 Section 17 - from which the term "emergency" actually came.
The latter provision states: "In times of national emergency, when the public interest so requires, the State may, during the emergency and under reasonable terms prescribed by it, temporarily take over or direct the operation of any privately owned public utility or business affected with public interest."
What does this have to do with preventing public demonstrations? What privately owned public utility or business could the administration be thinking of taking over? Broadcast media? Sea and air transport? Beats me.
Because of this kind of possible intervention, the atmosphere for business just got hazier. What can blacken it is bloodshed and a persistent clampdown on peaceful assembly.
The pressing need of the country is a return to normalcy. The sooner, the better.