Ong-art Klampaiboon, deputy Democrat leader, said the party will lodge a petition to the court soon through various channels.
He called on the caretaker government to revoke the Emergency Decree which, he claimed, has negatively impacted on tourism, foreigners' confidence in the country and the country's economy.
"The general election is held and it has been proven that people's rallies have not created any violent incidents, or state of emergency. The Emergency Decree is no longer necessary," he said.
Mr Ong-art said Thailand has yet to reach a resolution to the political stalemate now that elections have failed in some Bangkok constituencies and the South.
He said the government insisted on going ahead with the snap poll with an intention to stay in power as long as possible, to claim people's support, and to use the election results to justify its administration in the international community.
He said the Democrat Party, though boycotting the polls, will carry on its political activity on national reform and encourage public participation.
The Constitution Court last week rejected a petition by former Democrat MP Thaworn Senneam to nullify the Emergency Decree, imposed since Jan 22.