The proposed anti-secession law, read out for the first time before the ceremonial National People's Congress, doesn't say what specific actions might invite a Chinese attack.
"If possibilities for a peaceful reunification should be completely exhausted, the state shall employ nonpeaceful means and other necessary measures to protect China's sovereignty and territorial integrity," Wang Zhaoguo, deputy chairman of the NPC's Standing Committee, told the nearly 3,000 NPC members gathered in the Great Hall of the People.
Beijing claims Taiwan, split from China since 1949, as part of its territory. The communist mainland repeatedly has threatened to invade if Taiwan tries to make its independence permanent, and the new law doesn't impose any new conditions or make new threats. But it lays out for the first time legal requirements for military action.
Taiwan's Mainland Affairs Council, which handles the island's China policy, said the law gives China's military "a blank check to invade Taiwan" and "exposed the Chinese communists' attempt to use force to annex Taiwan and to be a regional power."
The island's vice president, Annette Lu, accused Beijing of violating international norms for peacefully resolving disputes, as Taipei prepared for an invasion.
Large-scale military exercises would be held from mid-April to August, with troops practicing knocking down Chinese missiles and fighting communist commandos, said Taiwan's Defense Ministry spokesman Liu Chih-chien.
Mainland lawmakers immediately expressed support for the anti-secession measure, which is sure to be passed when they vote March 14. The NPC routinely approves all legislation already decided by Communist Party leaders.
"We must join hands and absolutely not allow Taiwan to separate from China," said Chang Houchun, a businessman and NPC member from southern China's Guangdong province.
Chinese officials say the law was prompted in part by Taiwanese President Chen Shui-bian's plans for a referendum on a new constitution for the island that Beijing worries might include a declaration of independence.
Chen says the vote would be aimed at building a better political system, not at formalizing Taiwan's de facto independence.
Chinese leaders have appealed in recent months for Taiwan to return to talks on unification. But they insist that Taiwanese leaders first declare that the two sides are "one China" — a condition that Chen has rejected.
Beijing favors a "one country, two systems" solution for Taiwan, which was the model used when Hong Kong reverted to Chinese sovereignty in 1997.
In Taipei, Chen Chin-jun, a legislative leader of the ruling Democratic Progressive Party, said the island wants peace and trade with China.
However, he said, "We will not accept any resolution to allow the Chinese Communists to unilaterally decide Taiwan's future, and it will only antagonize the Taiwanese."
China and Taiwan have no official ties and most direct travel and shipping between the two sides is banned. But Taiwanese companies have invested more than $100 billion in the mainland and the two sides carry on thriving indirect trade.
In an apparent attempt to calm Taiwanese public anxiety, Wang said the law promises that Chinese military forces would try to avoid harming Taiwanese civilians. He said the rights of Taiwanese on China's mainland also would be protected.
Until recently, China's military was thought to be incapable of carrying out an invasion across the 100-mile-wide Taiwan Strait. But Beijing has spent billions of dollars buying Russian-made submarines, destroyers and other high-tech weapons to extend the reach of the 2.5 million-member People's Liberation Army.
The United States has appealed to both sides to settle Taiwan's status peacefully, with no unilateral changes by either side. Washington is Taiwan's main arms supplier and could be drawn into any conflict.
The proposed law says Beijing regards Taiwan's future as an internal Chinese matter, rejecting "any interference by outside forces."
The United States has said it opposes any change in the status quo, but President Bush has promised in the past to help Taiwan defend itself.