A thorny legal issue in many asylum cases involving illegal immigrants from China arises from a simple biological fact: once here, immigrants frequently have children. Often they have more children than they would be permitted in China, where strict family-planning practices limit married couples to one or two children. When threatened with deportation, some of them claim asylum on the grounds that if returned to China, they could be sterilized for the reproductive freedom they had here.

Such asylum requests received a significant boost by two recent decisions from a federal appellate court in New York. The decisions represent a judicial about-face for the 2nd U.S. Circuit Court of Appeals, which in August, 2005 had told a Chinese immigrant who fathered two American-born children that his fear of sterilization upon deportation was “speculative at best.”

With the decisions — one was issued in September and the other a week ago yesterday — the court allows for the possibility that regional governments in China count the American-born children of Chinese immigrants against the quota of children each couple can have. In the decisions, the court ordered the Justice Department’s Board of Immigration Appeals to review Chinese documents suggesting Chinese nationals can be punished for the children they have abroad.

China’s family planning policies have produced a flow of asylum cases since Congress broadened the definition of a refugee in 1996 to include those persecuted under their home country’s family planning policies. Last year, Congress lifted a cap that limited to 1,000 the number of immigrants who could receive asylum on the basis of family planning claims.

China accounts for the vast majority of asylum claims involving claims that deportation could ultimately mean sterilization. Because family planning regulations and enforcement vary by region, the courts have had difficulty judging the likelihood that a Chinese immigrant would be sterilized.

The 2nd Circuit’s recent about-face followed its review of several purported Chinese documents submitted as part of an asylum application. The documents suggest that forced sterilization is in effect in the Fujian Province, which is opposite Taiwan and is a source of emigrants from China. The documents, purportedly from family planning administrations in the Fujian province, say “the reproductive behavior” of Chinese nationals abroad will be sanctioned according to family-planning rules back home in China, according to the decision.

Another document that the court considered was the Q&A handbook from the Family Planning Administration of Changle City in the Fujian Province. This document, the court ruled, “lends powerful potential support to” to the claim for asylum ” because it states that a parent of two children … would, on her return, be subject to forced sterilization, even if one were born outside of China,” the decision reads.

In light of the documents, the 2nd Circuit ordered the Board of Immigration Appeals to review again the case of an immigrant, Shou Yung Guo, a mother of two, including an American-born child. Previously, the BIA had rejected her asylum claim. The court also chastised the BIA for ignoring the documents.

“Since the documents Guo submitted are so self-evidently material, we are hard-pressed to understand how the BIA could have dismissed them so casually,” the judges on the panel, Thomas Meskill, Robert Sack, and Barrington Parker, wrote.

The Guo decision was followed last week by a decision much talked about by immigration attorneys. The latest case, which cites the same documents, suggests the court is taking a new approach to these asylum cases.

In that decision, a different panel of three judges considered the case of Tian Ming Lin, the father of two American-born children, also from Fujian Province. Lin, afraid he himself would be sterilized, said that his own mother had been sterilized following the birth of her third child, according to court documents. The court sided with Lin.

“Returning a person to a part of China where he or she will face an officially sanctioned policy of forced sterilization, however, would appear to violate United States law, which expressly holds that a person with a well-founded fear of forced sterilization is a refugee eligible for asylum,” the court wrote. The judges deciding the Lin case were Rosemary Pooler, Sonia Sotomayor, and Robert Katzmann.

The court’s decisions in the two cases caused at least one anti-immigration activist to question whether courts should be benefiting immigrants who manage to evade authorities or appeal deportation orders for long enough to have large families.

The director of special projects for the Federation of American Immigration Reform, Jack Martin, said the cases gave illegal immigrants from China “a new option.”

“The illegal immigrant from China can protect himself from deportation by managing to stay in the United States long enough to have children,” Mr. Martin said.

But a New York lawyer who represents Chinese immigrants facing deportation, Gary Yerman, said it would be a mistake to see these decisions as a reward for illegal immigrants who manage to evade authorities.

“People aren’t having children so they can use them as props.” Mr. Yerman said. “We’re talking about people who are in their 20s or 30s and through the natural matriculation of life they are having children. They are not trying to dupe the law.”

Mr. Yerman praised the decisions in Lin and Guo as establishing “a modicum of consistency.”

The 2nd Circuit has expressed some discomfort with its recent approach to these cases. In another case involving a Chinese asylum seeker, decided last month, the court asked the BIA to decide, as a matter of policy, whether having two children was enough alone to support an asylum application based on fear of sterilization.