The Grand Ayatollah Makarem Shirazi answered a question about remaining silent when it can be regarded as approval or strengthening the oppressor.
Question: Is it allowed to remain silent when it can be regarded as approval or strengthening the oppressor?
The Grand Ayatollah Makarem: Whenever the silence of religious scholars or others can strengthen or approve the oppressor, or give courage to the oppressor for other forbidden cases; it is Wajib to speak the truth and deny the falsehood, even if the effect is not immediate.
source : shafaqna.com