Thousands of Taiwanese have gathered in front of the chief executive's office to denounce a government plan for reforming the pension system.
Military personnel, teachers, police and civil servants protested the plan outside the presidential office in the capital, Taipei, on Sunday.
Police said about 12,000 people were estimated to have taken part in the protest rally.
The demonstrators, barricaded from the presidential office by rows of wired fences and barriers, chanted slogans such as "Tsai Ing-wen step down" and "We protest the Tsai government."
The protesters called the reform plan "government bullying" and "majority tyranny."
Tseng Kwang-ming, 70, a retired teacher who attended the rally, said the plan would cut his monthly pension by almost half from T$60,000 ($1,900) currently.
"This plan is so shocking to all of us. The government is having financial problems. Everyone should be willing to share the burden, not just us."
The angry protesters say the new system will ruin their retirement plans and demonstrates the incompetence of President Tsai Ing-wen.
Vice President Chen Chien-jen announced the pension reform plan this week. It would delay a default in payments to retirees by a decade.
Tsai's government says the plan is "urgent" given the limited national and social resources.
A successful reform will be crucial for President Tsai, whose popularity has hit an all-time low since taking office last May.
Slower economic growth and a rapidly aging population have forced the government to launch a quick shake-up in the pension system.
Tsai, in opening remarks at the conference, where government officials are discussing the plan with public servant representatives, said, "The point is to ensure that Taiwan's pension system will remain a solvent system which the government can afford while also ensuring that retirees can get their pensions."