Speaking to reporters here, CPI(M) executive committee member (Tamil Nadu) T Murugan said Singh's recommendation as a Rajya Sabha MP for issue of passport to Khan in 1997 was ''proof'' of his close links to him.
"All issues relating to Iqbal Singh should be enquired into. The Enforcement Directorate and CBI should lose no time in initiating an enquiry", he said.
Murugan said the party would stage black flag demonstrations against Singh wherever he participated in functions here.
He came down on the ''inefficient'' Congress government for allegedly issuing a No Objection Certificate to a medical college to be set up at Karaikal by a trust, which reportedly has his relatives in it.
"Even Chief Secretary R Chandramohan's clarification later on the essentiality certificate issued to the trust to start the college were inspid," he alleged.