The outfit, in a letter to SGPC president Avtar Singh Makkar, had asked him to explain on what basis the decision was taken, Dal Khalsa chief H S Dhami said in a statement here.
Dhami alleged that Santa Singh had challenged the supremacy of the Akal Takht and urged the SGPC to withdraw its decision to install his portrait in the museum.
Santa was excommunicated by the Akal Takht from the Sikh Panth in 1984 for undermining and challenging the supremacy of Akal Takht.
The ex-communication was revoked in 2001 after he admitted his "sin" and accepted the punishment for violating