When New York lawmakers passed the so-called Green Light Law in June, it was hailed a landmark victory by those who had fought for the measure for more than two decades.

The law makes New York one of 14 states that allow undocumented immigrants to obtain driver’s licenses, which proponents argue will help them avoid deportation for relatively minor offenses, such as traffic violations.

But the change has been met with resistance from county clerks in conservative areas of upstate New York, who are now setting the stage for a political clash when the law takes effect next month. Some say they will refuse to issue the licenses, while others are also threatening to call Immigration and Customs Enforcement if applicants show up without documentation.

“If you come into my facility and you have done something illegal, it is my obligation to report you to the appropriate authorities, whether you’re a citizen or not,” said Robert L. Christman, the Allegany County clerk.