The United States, United Nations and the Commonwealth have also raised concerns that the move to impeach Chief Justice Shirani Bandaranayake, on charges including financial irregularities and failure to declare assets, threatens the independence of Sri Lanka's courts.
The Supreme Court has declared the impeachment attempt illegal, and thousands of protesters marched from the Supreme Court to the commercial heart of the capital despite heavy rain and counter protests by pro-government supporters.
They were prevented by police from proceeding to parliament, which began a debate on whether to impeach Sri Lanka's first female chief justice and will hold a final vote today.
Government and judiciary have been on a collision course since President Mahinda Rajapaksa's ruling party filed an impeachment motion against Bandaranayake on November 6.
A month later, a parliamentary panel found her guilty of irregularities.
The government, which has a two-thirds majority, needs 113 out of 225 votes to remove Ms Bandaranayake.
The International Commission of Jurists said the move had brought the country "to the brink of a constitutional crisis."