Mumbai: Shiv Sena chief Uddhav Thackeray was invited for the swearing-in ceremony of H D Kumaraswamy as Karnataka chief minister, but "politely declined" as he was busy with campaigning for the upcoming Palghar Lok Sabha bypoll in the state, a senior party leader said today.

Former prime minister and JD(S) leader H D Deve Gowda called Thackeray yesterday and extended an invite for his son's oath-taking ceremony, Sena MP Sanjay Raut told media.

"However, Uddhavji politely declined and extended his best wishes to the new government," he said.

"Uddhavji told him he was very busy with the Palghar bypoll and hence, would not be able to attend the ceremony. These elections are very important for us," Raut added.

The by-election to the Palghar Lok Sabha seat is scheduled to be held on May 28.

A JD(S)-Congress coalition government headed by Kumaraswamy will be sworn-in later today at a ceremony to be attended by a galaxy of opposition leaders and chief ministers, a development that could could be a harbinger for a broad-based anti-BJP platform before the Lok Sabha polls next year.

The Congress has 78 lawmakers in the lower house of Karnataka against 37 of the JD(S).

The BJP has dubbed the Congress-JD(S) alliance "unholy" and claims the government will not complete its full term.

It has decided to boycott today's oath-taking ceremony and said it will observe "anti-popular mandate day" to protest the formation of the coalition government in the southern state.