The speaker of the Uttar Pradesh state assembly in India has said the 40 rebel legislators will be treated as a separate group following court orders.
Mr Yadav proved his majority after 40 BSP rebels defected
Mata Prasad Pandey also said the rebels could not go back to the Bahujan Samaj Party (BSP), which they left in 2003.
The Samajwadi Party came to power following the politicians' defection.
The move came after a court ruled the speaker in 2003 had not followed rules in recognising the defection, and ordered fresh hearings in the case.
The BSP says the defection of its members was illegal.
The state assembly elections in Uttar Pradesh, India's most populous state, are due next year.
Vote of confidence
Mr Pandey said he would decide the fate of the rebel legislators after a proper hearing.
BSP leader Mayawati wants Mr Yadav to resign
Four of the rebel legislators said earlier on Wednesday they had decided to go back to the BSP following Tuesday's decision by the Lucknow High Court.
Two rebels, who are junior ministers in the current government, resigned from their posts.
Following the court ruling, Chief Minister Mulayam Singh Yadav called a vote of confidence in the state assembly, which all main opposition parties boycotted.
He was backed by 207 members in the 403-seat house.
The defection of the 40 BSP legislators helped Mr Yadav to win a majority, leading to the formation of the current Samajwadi Party government in 2003.
Opposition parties have demanded the chief minister's resignation, saying he has no moral right to continue.
The BSP says the manner in which its members defected and joined the Samajwadi Party was illegal under India's anti-defection law.