The decision came hours after Mulayam expelled party general secretary Ram Gopal Yadav for six years while terming the decisions taken in the national executive meet as "unconstitutional and illegal".
"This meet was called without consulting the national secretary of the party and the proposal passed in it is illegal. Stringent action will be taken against the people involved in it," said the letter issue by Mulayam.
Earlier in the day, Ramgopal called on party leaders and workers to declare Uttar Pradesh Chief Minister Akhilesh Yadav as the president of the party.
In a dramatic turn of events, the Samajwadi Party had on Saturday revoked the expulsion of Chief Minister Akhilesh Yadav and Ramgopal Yadav, a day after they were ousted from the party for six years over anti-party activities.