The Chinese parliament is expected to approve the bill and pass the anti-secession law on 14 March, giving the mainland the right to attack what it considers a renegade province.
But Taiwan Prime Minister Frank Hsieh warned on Tuesday that it would not take it lying down.
"If China passes a law that allows them to use force against us at any time, and includes us as part of the People's Republic of China, I am in favour of revising [the constitution]," Hsieh said in response to a lawmaker's
He was asked by the opposition lawmaker whether he would support revising articles in the constitution that deals with Taiwan's sovereignty and territory.
"Using non-peaceful means to stop secession in defence of our sovereignty and territorial integrity would be our last resort when all our efforts for a peaceful reunification prove futile"
Wang Zhaoguo, China National People's Congress vice-chairman
Hsieh, who took office in January after the previous cabinet resigned after disappointing election results, did not give details on how the constitution may be revised, saying it would depend on ties with Beijing at the time.
Constitutional re-engineering is a politically sensitive issue as Taiwan's constitution was written in China and brought to the island by the Nationalists in 1949, when they lost a civil war to the communists.
Beijing considers a new constitution to be tantamount to a
dangerous push for statehood by Taiwan, even though Taiwanese President Chen Shui-bian has repeatedly pledged that any changes would not involve a new name, territory, or other sovereignty issues.
In Beijing on Tuesday, Wang Zhaoguo, vice-chairman of the National People's Congress, or parliament, reiterated the government's willingness to use military force against Taiwan, but only as a last resort, preferring the alternative of reunification using the "one country, two systems" model adopted by Hong Kong.
"Using non-peaceful means to stop secession in defence of our sovereignty and territorial integrity would be our last resort when all our efforts for a peaceful reunification prove futile," Wang told lawmakers.
Wang stressed that China was entitled to use force to check secessionist activities, "in the event that the Taiwan independence forces should act under any name or by any means to cause the fact of Taiwan's secession from China".
China could also pursue the military option if "major incidents entailing Taiwan's secession from China should occur or peaceful reunification should be completely exhausted".
Despite the belligerent tone of Wang's presentation of the draft legislation, Foreign Minister Li Zhaoxing said the law was primarily meant to bring about peaceful reunification.
"This law is for the promotion of peace in our country. It is
for the peaceful reunification," he told reporters.
Taiwan's Chen (L) and Hsieh may
change the island's charter
Wang also argued that China's basic policy remains "peaceful reunification and one country, two systems", referring to the formula under which Hong Kong has been governed since its return from British rule in 1997.
While Wang said the system would allow "a high degree of flexibility by taking into account Taiwan's past and present circumstances", Taiwan's President Chen has previously rejected the proposal.
Critics have also lambasted Beijing for undue interference in Hong Kong.
The anti-secession legislation has sparked concern that it could end the "strategic ambiguity" over Taiwan's status that has ensured decades of relative calm in the Taiwan Strait.
Last month, the United States and Japan jointly issued a statement which described Taiwan as a common security issue amid China's military build-up.
Beijing on Tuesday took a swipe at "outside forces" interfering in its internal affairs.
"Solving the Taiwan question and achieving China's complete
reunification is China's internal affair," said Wang. "On this
question we will not submit to any interference by outside forces."