Beijing's new anti-secession law can hardly fail to exacerbate existing tensions in U.S.-China relations. That's because it undermines the tacit understanding the two countries have long shared over Taiwan, under which Beijing pretended to pursue a policy of peaceful unification while Washington pretended to pursue a one-China policy.

Beijing's side of that understanding has been called into question by the anti-secession law, the text of which was released yesterday. It not only refers to the use of "nonpeaceful means," but sets open-ended circumstances under which China can resort to such measures. These include simply deciding that "possibilities for a peaceful reunification should be completely exhausted," something which China could redefine to mean whatever it wants.

Also called into question are Beijing's repeated claims that the bill is simply a response to the Chinese public's clamor for a national-unification law. That assertion is belied by the unprecedented secrecy surrounding the legislation's text prior to its public release yesterday. Fewer than 100 Chinese legislators, party officials and scholars in Beijing had access to drafts of the bill prior to its release, and none were permitted to make copies or even notes about its wording. All were warned that any leaks would be treated as theft of state secrets and punished accordingly.

But, despite the lack of details, alarm bells have already been ringing in Washington for many months about the bill's likely impact on U.S.-China relations. The Bush administration has been closely watching the issue ever since it was first publicly raised last May, during a meeting in London between Chinese Premier Wen Jiabao and a group of overseas Chinese citizens. In private, U.S. officials repeatedly made clear to Beijing that any attempt to "redefine" the status quo in the Taiwan Strait would force the administration to reassess its policy on Taiwan.

Such warnings were conveyed in stringent terms after China publicly confirmed its intention of introducing an anti-secession law last Dec. 17, less than a week after Taiwanese voters had removed any conceivable urgency for such a bill by denying a majority to pro-independence parties in Taiwan's parliament, the Legislative Yuan.

That message was conveyed to Chen Yulin, China's top official on Taiwan affairs, when he visited Washington in early January. Both the White House and State Department told him in no uncertain terms that the U.S. viewed the "anti-secession" law as an unhelpful escalation in cross-Strait rhetoric. Later that month, Deputy Undersecretary of Defense Richard Lawless and Deputy Assistant Secretary of State Randall Schriver traveled to Beijing and reiterated Washington's concerns. They warned that Washington was beginning to see the "continuing substantial increase" in China's military capabilities as evidence that Beijing was preparing for an armed showdown. But they got little joy from their Chinese host, Maj. Gen. Zhang Bangdong, who recited a Chinese proverb. "The tree may prefer tranquility but the wind will not subside," he said warning that the winds of independence blowing from Taiwan could not be ignored.

Rebuffed in private, the Bush administration went public with its concerns last month. Central Intelligence Agency Director Porter Goss told a Feb 16. Senate hearing that Beijing's military modernization buildup, "could tilt the balance of power in the Taiwan Strait" and "threaten U.S. forces in the region." Three days later, U.S. Secretary of State Condoleezza Rice and Defense Secretary Donald Rumsfeld broke new ground in a statement of "common strategic objectives" with their Japanese counterparts, Foreign Minister Nobutaka Machimura and Defense Minister Yoshinori Ohno. For the first time in the U.S.-Japan alliance's near half-century of existence, the two countries listed Taiwan among their common strategic objectives. Although the wording was anodyne, referring simply to "the peaceful resolution of issues concerning the Taiwan Strait through dialogue," it was enough to prompt furious protests from Beijing.

Now, with the text of the bill having finally been made public, Washington will be studying it closely to see whether Beijing has irrevocably abandoned any pretense of continuing to pursue a policy of peaceful reunification. The Bush administration hopes that, despite all the rhetoric, in the end the Chinese leadership will opt to ease tensions rather than enflame them.

But if it becomes clear beyond doubt that Beijing has chosen to abandon its side of the tacit understanding over Taiwan that has persisted for decades, then there will be little reason for the U.S. to persist in its side. In the past, it suited Washington's purposes to pretend it had a one-China policy without drawing attention to the fact that this does not mean (and has never meant) that the U.S. recognizes Beijing's territorial claims to Taiwan.

Now that Beijing's aggressive action in tabling the anti-secession bill has changed the equation, it is time for a rethink.

John Tkacik is research fellow for China, Taiwan and Mongolia at the Heritage Foundation, Washington.