He had made his intention clear last Monday, the day when another senior BJP leader Jaswant Singh filed his nomination from Rajasthan's Barmer seat as an independent candidate.
Choubey said that he will also campaign against Modi who is contesting from Varanasi.
He said that he was hurt by the way the BJP is treating its stalwarts like Vajpayee, L.K. Advani and Jaswant Singh.
"I cannot tolerate humiliation to Vajpayee, Advani and Jaswant in the party," he said.
Chaubey was elected for the first time from Buxar parliamentary constituency in 1996. He represented the seat continuously till 2009 when he lost to RJD leader Jagadanand Singh by 2,000 votes.
