Taiwan's First Lady filed a counter libel suit against an opposition presidential candidate on Monday, turning election rivalry into a legal stand-off as an opinion poll put the two sides neck and neck.
With each side accusing the other of corruption, Lien Chan, chairman of the main opposition Nationalist Party, sued President Chen Shui-bian on Friday.
Chen's wife, Wu Shu-chen, hit back on Monday.
But while Lien's suit was only symbolic because the president cannot be subject to such legal action, Lien himself has no such protection.
"What makes me most angry is he (Lien) accused the head of state of corruption without any evidence," Wu told reporters.
Lien's Nationalist Party, which ruled Taiwan for 50 years until being routed in the 2000 presidential election, has said the value of stocks and bonds owned by Chen and his family soared more than 100 percent over the past three years, suggesting corruption.
The Nationalists have accused Chen of taking kickbacks.
Both sides have denied the allegations.
An opinion poll conducted by the mass-circulation China Times newspaper showed support for Chen and Lien tied at 35 percent each ahead of the March 20 election, with the balance of voters undecided.
The newspaper said Chen continued to face pressure over his controversial plan to hold a referendum calling for China to dismantle missiles aimed at the island.
Tension across the Taiwan Strait has been simmering since November when Taiwan passed the referendum bill which China sees as a move towards independence. Beijing has threatened force if Taiwan drags its feet on reunification or declares statehood.
The Nationalists fled to Taiwan from China at the end of a civil war in 1949, and Beijing regards the island as a breakaway province.