Describing the hugely popular actor as a "true nationalist", Thackeray attacked the "Congress's allergy towards him".
Labelling the controversy over Bachchan as immature, Thackeray said in an editorial in the party mouthpiece Saamna that the actor was not a "thief, dacoit or terrorist" to be subjected to such "allergic" behaviour.
"All this merely because Bachchan is the Brand Ambassador of Gujarat and he was earlier the Brand Ambassador of Uttar Pradesh. That too, by the Congress which has made Sonia Gandhi the party's 'Brand Ambassador' though she accepted Indian citizenship 17 years after her marriage with Rajiv Gandhi," he pointed out.
A section of the Mumbai Congress had questioned the wisdom of inviting Bachchan to the inauguration of the second carriageway of the sea link in which he was seated next to Chief Minister Ashok Chavan.
Thackeray said that Bachchan was a true nationalist who would sacrifice anything for India but Congressmen were more interested in promoting Shah Rukh Khan who had supported the participation of Pakistani players in the Indian People's League (IPL) cricket tournament.
The Sena chief said that personalities like Bachchan, Lata Mangeshkar, Sunil Gavaskar and Sachin Tendulkar occupied top slots in their respective fields because of their merit and hard work, unlike the politicians.
"They are not dependent on some party leadership for retaining their chair. Nobody can unseat these personalities. But nobody knows when Chavan and his ilk can be dumped into the dust bin of politics," he said.
Thackeray lauded the Nationalist Congress Party (NCP) for inviting Bachchan to the function, saying that it added to the glory of the event.
Thackeray said that Chief Minister Chavan was now worried about sharing the dais with Bachchan at the concluding ceremony of the Marathi Literary Conference in Pune Sunday.
"Why this allergy towards Bachchan and treating him like an 'untouchable' if he is the Brand Ambassador of Gujarat?" Thackeray wondered.
He said if the Maharashtra leaders had concern for the state, then the Tatas and Ambanis would not live in Mumbai and make all their investments in Gujarat.
"Amitabh hasn't committed a crime by attending the event. Bachchan belongs to this country and will remain so, and for this he does not need the certificate of some Sonia Maino," Thackeray said.