Jayasuriya told the parliament that the apex court had determined that the certain clauses of the 20th Amendment is inconsistent with the Constitution. Therefore, it could only be adopted with 2/3rd parliamentary majority and a referendum.
The 20th Amendment seeks to hold election for all nine provincial councils on a single date.
The unity government was pushing for the 20th Amendment in order to postpone the elections by an year, citing the need to have all nine elections for provinces on a single day.
In the history of provincial council elections since 1988, elections for the 9 provinces have been always held on a staggered basis. Two of the councils end their terms this month while one of them ends its term on October 1.
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Elections Commission Chairman Mahinda Deshapriya said he would announce on October 2 the polling date for three councils - the south western, eastern and north central councils.
He said the elections could be held on December 9. If held it would be the first polls test of the unity government headed by President Maithripala Sirisena and Prime Minister Ranil Wickremesinghe.
The opposition accused the government of postponing elections for the fear of losing.
The government had postponed the elections for over 330 local councils in the island nation since 2015 for want for electoral reform.