"We appeal to the military's and police's conscience to stand on the side of the people and their families", writes opposition leader María Corina Machado and presidential candidate Edmundo González Urrutia in a long statement.
"We won this election without a doubt", they write.
"Now it's up to all of us to respect the people's voice."
Shortly after the appeal was published, the country's Attorney General announced that the two are being investigated for subversive activities and rebellion.
They are also accused of "incorrectly announcing a winner of the presidential election other than the one proclaimed by the national electoral commission, the only body qualified to do so".
The regime-loyal electoral authority proclaimed sitting President Nicolás Maduro as the winner of the election on July 28, but the result is being questioned both within the country and by leaders around the world.
According to the opposition, protocols collected directly from over 80 percent of the polling stations show that González Urrutia won the election with a significant majority.
The regime, despite international pressure, has still not publicly disclosed the full result to prove that Maduro won. On Monday, the electoral authority announced that the result had instead been submitted to the Supreme Court.
Both González and Machado are in hiding after threats from the regime that they will be arrested and imprisoned.
