The lex Cassia tabellaria was a Roman law, proposed by the tribune of the plebs Lucius Cassius Longinus Ravilla and enacted in 137 BC. It extended the secret ballot for trials in the popular assembly.
The secret ballot had been introduced the for the election of magistrates by the lex Gabinia in 139 BC.
It is thought that this law was adopted following the acquittal that L. Aurelius Cotta obtained by corrupting the judges in 138 BC.
Subsequent improvements or extensions to the law were the lex Papiria (131 BC), the lex Maria and lex Caelia (107 BC), all aimed at limiting corruption. Together these laws are called leges tabellariae.
The law introduced secret ballot to trials conducted in the popular assemblies, with the exception of treason cases..