Getting your Trinity Audio player ready...

U.S. border agents have stepped up scrutiny of Americans returning home from Mexico, slowing commerce and creating delays at border crossings.

It is part of a dress rehearsal for new rules, to take effect in January, that will require Americans to show a passport or other proof of citizenship to enter the United States. The requirements were approved by Congress as part of anti-terrorism legislation in 2004.

Border officials said agents along the southern border are asking more returning U.S. citizens to show a photo identity document. Agents are also increasing the frequency of queries in which they check a traveler’s information against law enforcement, immigration and anti-terror databases.

The new policy is a big shift after decades when Americans arrived at land border crossings, declared they were citizens and were waved on through. Since enforcement was intensified in August, wait times at border stations in Texas have often stretched to two hours or more, discouraging visitors and shoppers and upsetting local business.

The delays could remain a fact of life across the southern border for the next few years, border officials said, at least until new security technology and expanded entry stations are installed and until Americans get used to being checked and questioned like foreigners.

Ralph Basham, head of Customs and Border Protection, the agency that manages the borders, said longer waits are a result of added security measures at border stations that in many cases are outmoded and facing surging traffic.

The longer lines along the Mexico border have been especially unsettling in El Paso, a border city long comfortable in its marriage to Ciudad Juarez, the Mexican city on the other bank of the Rio Grande.

“We are Americans who live at the border, with our economy and livelihood that depend on moving efficiently back and forth,” said Maria Luisa O’Connell, president of the Border Trade Alliance, which represents border-area businesses. “Now suddenly we have measures that make it less efficient but don’t make us any safer.”