Wickremesinghe's United National Party (UNP) is set to hold a protest on Tuesday in the capital, Colombo.
"We are calling upon all sections of the society who believe in democracy and rule of law to gather and protest," Champika Ranawaka, a former minister said.
Mangala Samaraweera, the ex-finance minister under Wickremesinghe said, "This was a constitutional coup and it is our duty to protect democracy and sovereignty of people".
Speaker Karu Jayasuriya urged the president to let Wickremesinghe prove his majority support on the parliament floor.
The supporters of Rajapaksa, a former president, are confident that he would be able to prove majority support on the parliament floor as they are sure that members of Wickremesinghe's UNP would defect.
"We are waiting for more UNP members to join us. We have the numbers," Lakshman Yapa Abeywardena, a Rajapaksa loyalist, said.
Wickremesinghe has said that he still commands the majority. However, he suffered a setback after four lawmakers from his party, who had pledged allegiance to him in the public, took a U-turn and accepted ministerial positions in the Rajapaksa government.
"We have the majority despite four of them joining Rajapaksa," Ranjith Madduma Bandara, an ex-minister, said.
Speaker Jayasuriya has called for a meeting of all party leaders to assess the current political situation. At least 128 members had written to him calling for reconvening of parliament.
Jayasuriya has insisted that the issue needs to be settled within parliament.
The crisis turned deadly on Sunday when the bodyguard of a former cabinet minister fired on a crowd, killing at least one person and wounding two others.
Under Sri Lanka's constitution, the president, who maintains executive powers, can appoint a new prime minister once the current premier has lost control of parliament.
Wickremesinghe argues he cannot legally be dismissed until he loses the support of parliament. His party, which holds a plurality of seats in the 225-member assembly, was prevented from holding a vote when Sirisena abruptly suspended parliament on Saturday until 16 November.
Wickremesinghe claimed in a Facebook post on Monday he had obtained the signatures of 126 MPs calling for parliament to be returned immediately to end the political standoff.
Both camps are working to secure their numbers in parliament.
Rajapaksa's tenure as president was marred by allegations of authoritarianism, corruption and human rights abuses, especially against the country's Tamil minority.
He was defeated at the 2015 presidential elections when Wickremesinghe and Sirisena formed an unlikely coalition, and their government initiated several investigations into alleged Rajapaksa-era crimes.
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