Mr Somchai, the commissioner in charge of election management, said the meeting is scheduled for 10am.
He said the prime minister had been asked to inform the EC if she was not available for tomorrow's meeting, so the EC could then seek an appointment with her on Monday or Tuesday, or whenever she is available.
If Ms Yingluck assigned someone else to represent her, that person must have the power to make a decision, otherwise there would be no talks, Mr Somchai said.
The commissioner said there were at least three important legal points for discussion and he would disclose them after a meeting with the caretaker prime minister.
Mr Somchai said the EC also wanted caretaker Interior Minister Charupong Ruangsuwan to accompany Ms Yingluck to the meeting because the EC needed Interior Ministry officials to help organise the election.
"The request for a meeting with the prime minister was agreed by all five EC members, not myself alone.
"We EC members work and decide matters collectively," he said. "The way the prime minister is acting by refusing to meet with the EC and talking to the media instead is not helpful for society. The country is not something to play with. We have to help one another to bring about peace.
"The government should give due honour to the EC chairman, who is a joint caretaker [of the government]according to the royal decree on a House dissolution. She should let us know if she has a problem," Mr Somchai said.