The sudden decision of the 74-year-old Ramoowalia, who has had stint with different parties during his long political career, took the Akalis by surprise.
Ramoowalia, who is a former Union Minister, told PTI that he has resigned from the SAD and forwarded his resignation to the party chief.
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However, SAD's senior leader Mahesh Inder Singh Grewal said that "we are yet to receive resignation" of Ramoowalia, who was party's senior vice-president.
He said that he has great respect for SP supremo Mulayam Singh Yadav and could not say no when the latter himself rang him up yesterday and made the offer to him.
"I have great respect for Mulayam Singh ji. He rang me up yesterday morning and told me that the SP party wants my services. I could not say no. When I became Minister in the Union Cabinet in 1996, I was not even an MP then, at that time too it was possible because of Mulayam ji," Ramoowalia, who was SAD's senior vice-president, told PTI over phone.
Ramoowalia said that even UP Chief Minister Akhilesh Yadav had urged him to make the switch.
To a question, the elader said that he did not have any grudge against the Akali Dal.
"I just decided to make the move. I have submitted my resignation from the party. To all my colleagues in Akali Dal, I will say that I will always have great respect for them," he said.
SAD's General Secretary and MP Prem Singh Chandumajra said that Ramoowalia's decision to leave the party will not affect the Akali Dal.
"Ramoowalia did not have long innings in our party. Our party is like a sea. The Akali Dal is not dependent on any one individual," Chandumajra told PTI.
Ramoowalia was Labour Minister in the United Front government at the Centre headed by H D Deve Gowda. He was today sworn in along with 19 other ministers by UP Governor Ram Naik at Raj Bhawan in Lucknow following revamp of Akhilesh Yadav Ministry.
Ramoowalia started his political career way back in 1963 as a student leader and was also twice MP from Faridkot and Sangrur.
Over a decade back, he also floated his own party and named it as Lok Bhalai Party, but merged it with Akali Dal which he had joined four years back.
He lost during the 2015 assembly elections from Punjab when he contested from Mohali as an SAD candidate.
Ramoowalia also used to actively take up the cases of the women who were cheated and deserted by their NRI husbands.