The Save Malaysia movement's citizens' declaration demanding the removal of Prime Minister Najib Abdul Razak came under prompt attack from the government.
A spokesperson from the Prime Minister's Office called those who signed the declaration "opportunistic" and "desperate".
"Today, Tun (Dr) Mahathir (Mohamad) and his former enemies have demonstrated the depth of their political opportunism and desperation," the spokesperson said in a statement.
The statement came a few hours after Mahathir, former deputy prime minister Muhyiddin Yassin, and key opposition and NGO figures inked the declaration .
"There is an existing mechanism to change the government and prime minister. It's called a general election. And it is the only mechanism that is lawful, democratic, and fulfils the people's will," the statement said.
The removal of Najib from office is one of the demands listed in the 37-point declaration.
"In 2013, the Malaysian people expressed their will and elected the current government led by Najib. If Mahathir wants to change the government, he must follow democratic process and await the next election, in line with Malaysia's laws and the federal constitution," the spokesperson said.
Mahathir, former deputy prime minister Muhyiddin, opposition leaders and key NGO figures signed the declaration, which also called for steps to be taken to institute reforms.
No time for drama
Meanwhile, Umno information chief Annuar Musa sarcastically congratulated the opposition for finally accepting the leadership of an Umno man in the form of Mahathir.
"We congratulate DAP, PKR, Amanah and Bersih for finally accepting the leadership of a former Umno president, who we in Umno have for decades tried to convince them to accept," he said in a statement today.
Mahathir quit Umno on Wednesday in protest against Najib's leadership.
On a serious note, Annuar criticised Mahathir for forgetting what he taught Umno members when he was president.
He added that Umno has no time for "drama" and will focus on fulfilling its mandate to the rakyat.
Umno Youth vice-chief Khairul Azman Harun also ticked off Mahathir's move to join hands with the opposition, particularly DAP veteran Lim Kit Siang.
"Who is he (Mahathir) to demand leaders to step down (when) he works with Lim, a leader who has overstayed?
"If they have the courage, both of them who still refuse to retire should contest in the next general election," he said.
He said Umno Youth will remain disciplined and loyal to the current leadership.