Facebook has found itself drawn into an escalating political row in Sri Lanka as opposition MPs accuse the ruling party of using data to launch a crackdown.
In a letter to Facebook chief Mark Zuckerberg, the United National Party (UNP) said information gleaned from the social media site could be used against party members who use the site "in ways which are legally prohibited."
It urged Facebook to hide the identity of its supporters to protect them.
It came amid growing acrimony between members of the UNP and other parties due to a deadlock in the country's parliament.
The speaker of the country's parliament, Karu Jayasuriya, had books and chairs hurled at him in the chamber on Friday after he allowed a no-confidence vote against the prime minister to go ahead.
The no-confidence motion was passed, but Prime Minister Mahinda Rajapaksa refused to accept the result of the vote and insisted the speaker had no authority to remove him from his position.
The UNP letter, sent on Thursday, said: "It is very likely that officials from the current illegal administration... may ask Facebook for information on selected Sri Lankan users of Facebook that should rightfully be private.
"Such requests may include information on named individuals, geo locations and other identification details of users who view and post on these pages," the letter said.
"It is vital this information be safeguarded as the current illegal administration will most likely use these in ways which are legally prohibited."
UNP party spokesman Piyasena Dissanayaka said on Sunday that Facebook blocked its official page ahead of a public rally on Thursday but restored it on Saturday.
He said Facebook officials had not yet responded to the letter.
Facebook officials have also not yet responded to a request for comment by The Associated Press.
The UNP's Mr Jayasuriya had to get a police escort to get into the parliamentary chamber on Friday, with several officers among those injured as the unorthodox missiles were launched in his direction.
Opposition MPs were also among those hurt before proceedings got under way.
Mr Rajapaksa has only been in the job since 26 October after his predecessor Ranil Wickremesinghe was sacked by Sri Lankan President Maithripala Sirisenadue due to a disagreement over economic reforms.
The row has left the country without an official government, although Mr Rajapaksa has refused to stand down.
Mr Wickremesinghe also insists he is still prime minister.
On Sunday, Mr Sirisenadue summoned political leaders for talks in a bid to end the power struggle.
After the no-confidence vote against Mr Rajapakse on Friday, the second against him, Mr Wickremesinghe demanded his government be restored, but there has been no response from Mr Sirisenadue yet.
Both sides have warned that a prolonged period of instability could lead to violence, in a country that has not long emerged from civil war.