President Mahinda Rajapakse formally removed Fonseka's rank and medals and stopped his pension yesterday, a day after a court martial found him guilty of engaging in politics while in uniform.
"We do not accept the court martial process, but we are going to appeal to a civilian court against this decision," said Anura Kumara Dissanayake, legislator and spokesman for Fonseka's Democratic National Alliance.
Dissanayake said the government was trying to destroy the political career of Fonseka, who attained national hero status as the battlefield architect of the military victory over Tamil Tiger rebels in May last year.
The former four-star general, who quit the military in November to become an opposition politician, unsuccessfully challenged Rajapakse for the presidency in January elections.
Two weeks after his defeat at the polls, he was arrested and taken into military custody.
"The government wants to erase the memory of what General Fonseka achieved last year by ending the war," Dissanayake said. "He will remain in the minds of a grateful nation as a great hero.