He dubbed the decision of not calling Raja as a "serious omission."
Sinha, who is also a member of the JPC, said he would write to Prime Minister Manmohan Singh and Lok Sabha Speaker Meira Kumar that the intentions with which the panel was formed will not be fulfilled if Raja is not called as a witness.
Sinha, along with Left members of the Committee, has been backing Raja's plea to depose before the panel.
"...I saw in my mail a letter from A Raja to Chacko which casts serious doubts about the JPC's intention and in that letter Raja says he has written three or four letters to Chacko and in his replies, the JPC Chairman just acknowledges his letters and said nothing about his coming before the panel as a witness," he said.
Raja had made a written submission before the JPC in March and his response was recently circulated to committee members.
"I think it's a very serious omission that the Chairman of JPC is trying to make by not inviting Raja to depose before the JPC. Raja is right in casting aspersions on the intentions of JPC," he told reporters here.
The Opposition leader said he himself has "serious doubts" about the intentions of the government and some of the members who represent it in the panel on "whether the JPC is meant to arrive at the truth, uncover the truth or conceal the truth."
"I think we are proceeding in a direction where JPC will be used to conceal the truth rather than expose the truth. And it is a very serious matter. Unfortunately, the Chairman of JPC, despite our requests, he is not calling a meeting of the panel so that (the) matter could be thrashed out in such a meeting," Sinha said.
The BJP leader said he proposes to write to the Prime Minister and the Speaker bringing all these issues to their notice "and telling them very clearly that the intentions with which JPC was formed is not going to be fulfilled if we do not call the witnesses who are willing to appear and ready to appear before the JPC."