Suspended Trinamool Congress leader Mukul Roy on Wednesday resigned his Rajya Sabha seat and cited "lack of principle" as his compulsion to leave the party of which he was a founding member.He also said that he has not decided on his future plans yet."A party should have certain principles. Sometimes Trinamool Congress is with the BJP, sometimes they are with the Congress," Roy told the media at his residence here shortly after submitting his resignation from the Rajya Sabha seat to Vice President M. Venkaiah Naidu, who is also the Chairman of the upper house."We were very much a part of the NDA government once and joined hands with the BJP. Now the party thinks that the country cannot go ahead without the Congress. These things compelled me to leave the party with a heavy heart."We have formed a political party to fight against the Congress rule. That was the reason why Trinamool Congress was created. If we now think that the country cannot move without the Congress, I think there should be a merger between both the parties," he said.Revealing that he was in touch with the senior leadership of all the parties, Roy said he would take a decision about his future endeavours after Diwali."I have not taken any decisions about the future plans yet. I would go for a leave now. I will decide whether I would join any political parties or float a new party after the Kali Puja (Diwali)," he added.