Appointing a person convicted of contempt of court as the head of a state will create a constitutional crisis, JD(U) secretary general and Rajya Sabha member K C Tyagi said in a statement.
He added that the move should be called off for the sake of the dignity of the high office.
The BJP government at the Centre, according to him, had already damaged it by unethically removing governors since they have come to power.
Tyagi contended that Singh had given a wrong commitment to the Supreme Court as the chief minister of Uttar Pradesh that he would protect Babri Masjid.
The apex court, on October 24, 1994, found Singh guilty of filing a false affidavit and not taking enough measures to protect the Babri Masjid and sentenced him to a days imprisonment.
Tyagi said, If a person convicted of contempt of court is made the head of state, this will certainly create a constitutional crisis.
He suggested that the President seek legal advice on the matter.