The emergency decree is ready to be invoked if the planned shutdown of Bangkok turns violent, National Security Council secretary-general Paradorn Pattanatabut says.
Lt Gen Paradorn said a plan to deal with the protests has been presented to the Centre for the Administration of Peace and Order (Capo) and caretaker Prime Minister Yingluck Shinawatra.
The plan was formed during a meeting between police and the military, he said.
Soldiers will take care of security at key state agencies and police will contain any outbreaks of violence, he said.
"Whether or not the emergency decree is implemented depends on the situation at hand," Lt Gen Paradorn said. "If there is terrorism, threat to life, damage to private or state property, the prime minister will invoke it immediately."
Security officers predict a huge turnout of demonstrators on Monday, he said.
"We are worried violence will inevitably take place because some groups are bent on causing unrest," Lt Gen Paradorn said.
Speaking after a cabinet meeting yesterday, Ms Yingluck said each ministry must take care of itself and cooperate with security agencies to carry on its work.
She asked security officers to maintain peace and order using measures which least affect the public, and called on protesters to avoid areas prone to confrontation.
Deputy government spokeswoman Sunisa Lertpakawat said the premier had assigned Justice Minister Chaikasem Nitisiri and Labour Minister Chalerm Yubamrung to provide legal advice to the government if violence erupts.
Ms Yingluck also asked the ministers to exercise restraint and abide by the law, Lt Sunisa said.
Caretaker Deputy Prime Minister and Foreign Minister Surapong Tovichakchaikul told the cabinet the ministry will invite representatives from more than 60 embassies for a briefing today.
Suranand Vejjajiva, Ms Yingluck's secretary-general, said the emergency decree would be implemented in line with international standards.
In 2010, the Centre for the Resolution of the Emergency Situation, in line with the decree, did not require army officers to be in charge, he said.
Police can lead the response with back-up from the army, Mr Suranand said.
Ms Yingluck also told ministers to consider working from other locations if their offices are forced to close, he said. She urged the ministers to continue their work until the new cabinet is formed after the election, he added.
National police chief and Capo director Adul Saengsingkaew said he was worried the PDRC's shutdown attempt would lead to violence.
A combined force of police and military will provide security for important figures, including Ms Yingluck and cabinet members, he said.
Pheu Thai spokesman Prompong Nopparit yesterday dismissed a report that ousted prime minister Thaksin Shinawatra had set up a command centre in Hong Kong to guide the government through the attempted shutdown. Thaksin has not formed a command centre as he is not involved in politics, Mr Prompong said.
The caretaker government and security agencies are in charge of security, he said.