Bali Padyami Puja is celebrated on the fourth day during Diwali festival. In 2014, Bali Padyami date is October 24.
It is observed on the day after Deepavali Amavasya. Maha Bali, the King of Pathala loka (netherworld), is worshipped on this day. He was given a boon by Lord Vishnu to visit the earth once a year.
Kannada and Marathi people celebrate Balindra Puja to mark his arrival to the earth whereas Kerala people celebrate Bali Puja during Onam festival observed in Shravan month.
In some places, it is also celebrated as Vamana Jayanthi. Bali Chakravarthi had observed 99 sacrifices and about to perform his 100th Yagna. If he does that, he becomes Indra.
As per several sacred texts of Hinduism, Indra, Yama, Brahma and some other devas have posts. Indra is a post and the God who takes up the post is called Devendra. Thus, to avoid Bali to sit in the position of Devendra, Lord Vishnu was incarnated as Lord Vamana and banished Maha Bali into the netherworld.