Prime Minister Narendra Modi with Punjab Chief Minister Parkash Singh Badal during his visit to Amritsar in March. (Agence France-Presse)

On Sunday, when Prime Minister Narendra Modi launches his yoga day programme across the country, a state ruled by his ally will stay out of the celebrations. Punjab's ruling Akali Dal has decided to skip the event in what reflects souring ties between the long-time allies.Sources say Punjab Chief Minister Parkash Singh Badal is angry that PM Modi cancelled his proposed visit to the holy city of Anandpur Sahib this week. Home Minister Rajnath Singh will go instead.The state government is believed to have conveyed to the Centre that it cannot force students come to school during their vacations for the event. Most schools are on summer holidays till June 30.A state government circular asking for students' participation in the yoga event has not been forwarded to schools. NDTV has accessed the circular, which asks school children to join the yoga event between 7 and 7.35 am on Sunday.Ties between the BJP and Akali Dal have been strained over the recent transfer of terrorist Devinder Pal Singh Bhullar, a convict in the 1993 Delhi blast, from Tihar jail in the capital to Amritsar. The BJP alleges that it was not consulted on the decision. Bhullar's death sentence was commuted to life by the Supreme Court last year.Sources say PM Modi cancelled his Punjab visit after BJP leaders from the state discussed the Bhullar row and also expressed concern about what they alleged was the Akali Dal's religious agenda. Recent incidents like the death of a teen molested and thrown from a bus operated by the Badals have also reportedly rattled the BJP.The prime minister had recently accepted Mr Badal's invitation to attend the 350th anniversary on Friday of the holy town. But Punjab has been told that PM Modi has to host the President of Tanzania on the same day.