The Supreme Court of Sri Lanka ruled on Tuesday that the proposed amendment including the removal of the President's term limit was consistent with the country's Constitution.
The Court added that there was no need for a country-wide referendum on the 18th amendment and 2/3rd majority in Parliament was sufficient to pass it.
Meanwhile, PM D M Jayaratne tabled the 18th Amendment in Parliament on Tuesday amid a walkout by the opposition United National Party (UNP) inside the house and demonstrations outside.
According to reports, the bill was tabled amidst vociferous protests from the Opposition.
However, Speaker Chamal Rajapaksa maintained that since the Supreme Court has ruled that the amendment bill was consistent with the Constitution and that only a two thirds majority in Parliament was needed, it did not pose any problems with the tabling of the bill.
The amendment would be taken up for debate on Wednesday with a vote to be taken in the evening.
Ranil Wickremesinghe, UNP chief, gave a speech saying his party will not participate in the debate on the 18th Amendment.
The leftist Janatha Vimukti Peramuna (JVP) organised 'black day' demonstration at a busy Colombo junction to mark its protests against it.
Despite the protests, the government seemed set to get well over 150 votes required for a 2/3rd majority to pass the bill. It has already been assured by a number of Opposition members of parliament of support on the amendment.
One of the main minority parties, the Sri Lanka Muslim Congress (SLMC), part of broad opposition coalition during the Presidential and Parliamentary elections, has also pledged to support the government on the bill.