"We are seeking a court order on the suitability of this candidate because he is not eligible to be declared as a candidate," Foreign Minister Rohitha Bogollagama told reporters.
He said they would seek court action to have Fonseka ruled out of the race after the former four-star general was unable to vote in Tuesday's election because his name was not on the electoral list.
Responding to suggestions from ruling-party lawmakers that Fonseka could be disqualified, the country's independent election commissioner gave the opposition figurehead resounding backing in a statement earlier Tuesday.
"Not having one's name on the electoral list is not a disqualification," Dayananda Dissanayake said.
Bogollagama said the government would challenge this assessment.
"What the election commissioner has expressed is merely an opinion, but the courts have the ultimate authority to interpret the law," Bogollagama said. Asked if it was premature for the government to press legal action even before