TUCSON, Arizona - Tucson police officer Martin Escobar has worked to build relationships of trust in the working class Mexican-American neighborhood he patrols.

Tucson police officer Martin Escobar But after Arizona passed a state law in April cracking down on illegal immigrants, some residents stopped coming forward to report crimes like robberies and domestic violence, for fear of being arrested.

"Ask any officer ... You would not believe how many incidents go unreported ... even though the law has not gone into effect," said Escobar, 45, who has worked as a police officer in the city for 15 years.

The Arizona law requires state and local police, after making lawful contact, to determine the immigration status of any person they suspect is in the country illegally.

Escobar is one of two police officers in the desert state who have filed lawsuits in federal court to challenge the law, which takes effect on July 29.

The state law is backed by a majority of Americans, and by the two largest police unions in Arizona, a main corridor for drug and human smuggling over the border from Mexico.

In Tucson's gritty south side that Escobar patrols, more than half of residents are Hispanic. They include third- and fourth-generation Mexican-Americans, as well as immigrants.

In his suit filed in April, Escobar argues there is no "race-neutral criteria" to identify illegal immigrants. He says officers would inevitably apply the law "based on how a person talks or what they look like."

Escobar also argues that Tucson police have no authority to carry out federal immigration duties, and says the law would seriously impede investigations in the community he patrols.

"These are the people that are calling in something going on," said Escobar, a naturalized U.S. citizen who moved to Tucson with his Mexican family at age 5.

"And these are the same citizens who are not going to want to call, because the fact is they are going to want to avoid all contact whatsoever," he added.

'SERVE AND PROTECT'

Escobar's doubts about the state law are shared by several U.S. police chiefs and President Barack Obama's administration, which may file its own suit over the law.

Last week, a group of eight police chiefs from cities including Los Angeles and Tucson told U.S. Attorney General Eric Holder the state law would sap limited law enforcement resources and could lead to an increase in crime.

"When you enact legislation that makes any subset of that community feel like they are being targeted specifically or have concerns about coming forward and talking to police, that damages our capability to obtain information to solve the crimes," Tucson Police Chief Roberto Villasenor.

No hearing has been set for Escobar's lawsuit. In the meantime, his relations with fellow officers have been strained.

"Some officers don't speak to me any longer (and) I lost several friends because of the stand I took," Escobar said.

But he said he has no regrets: "I've always tried to do the right thing. ... Our motto is to 'serve and protect,' and that includes everyone."