Amid a crackdown on illegal immigration, two Dallas lawyers are urging illegal and legal immigrants and U.S. citizens of Hispanic ancestry to know their rights if stopped by traffic police in cities around Dallas.

Lawyers Domingo García and Fernando Dubove are threatening to file federal lawsuits alleging racial profiling and say they have about a dozen complaints from people who were stopped for traffic infractions and placed under detention by federal immigration agents.

But the lawyers said potential litigants wish to stay anonymous until they file a suit.

Know-your-rights campaigns have spread in cities with large foreign-born communities in the last two years. Among the lawyers' advice:

•Be careful when driving to avoid even the smallest infraction, such as not using a turn signal.

•If arrested by a police officer and then detained by federal immigration officers, the detainee has the right to bond, in most cases; to counsel for the immigration proceeding, paid by the detainee; and to an immigration hearing.

Mr. García said that a pattern was developing of U.S. citizens and U.S. legal residents being detained by immigration agents. Mr. García is a leader in the League of United Latin American Citizens, a group whose roots go back to the 1920s in the Rio Grande Valley of Texas, when Mexican-Americans fought for civil rights as U.S. citizens.

Mr. Dubove urged legal permanent residents to carry their "green cards," or residency documents, as required by law. And those who have pending applications for residency should carry proof of the application, he said.

The number of people held on suspicion of being in the U.S. illegally has increased, according to Immigration and Customs Enforcement, an agency of the Department of Homeland Security. In August, ICE officials said the national number had more than doubled to about 18,600 since October 2006. Officials did not have an updated count available Tuesday.

Last year, the issue of detentions after traffic stops roiled the city of Irving with protests against and for the police.

Police Chief Larry Boyd has denied his officers engage in racial profiling. He said police in Irving have stopped immigrants from 46 different countries but Latino immigrants make up the bulk of the foreign-born and, therefore, the bulk of those placed on immigration holds.

An ICE spokesman, Carl Rusnok, said it is "extremely rare" for U.S. citizens to be placed on a hold. And legal permanent residents can be deported, depending on criminal convictions.