They were sacked hours after Mulayam expelled Ramgopal Yadav for six years terming the decisions taken at the convention as "unconstitutional and illegal".
In a letter to Nanda, Mulayam said he took part in the "emergency national representatives' convention" which is not only "unconstitutional but also amounts to anti-party activities".
Agarwal has also been expelled from the party for taking part in the convention, a senior SP leader said.
"For taking part in the unconstitutional national representatives' convention and continuous involvement in anti-party activities, he is being removed from the post of national vice president. He also ceases to be a primary member of the party," the letter stated.
Nanda had chaired the national convention called by Ram Gopal Yadav that anointed Akhilesh the SP president, removed his uncle Shivpal Yadav as the state unit chief and expelled Amar Singh.