A government crackdown that found Chipotle Mexican Grill had hired hundreds of undocumented workers has turned Monty Moran, the burrito chain’s co-leader, into an unlikely champion of immigration overhaul.

Over the past year, Chipotle became the highest-profile target of an Obama administration campaign against employers of illegal workers.

In a so-called silent raid, Immigration and Customs Enforcement inspected the chain’s hiring records and found more than 500 undocumented workers, who had to leave the Denver-based company. It had to let go more than half of its 900 employees in Minnesota and lost others to federal scrutiny of outlets in Washington and Virginia.

The enforcement moves left some restaurants struggling to operate as managers rushed to train replacements. Finding qualified workers has become a continuing challenge, partly because word has spread that Chipotle has become part of a federal worker-screening program.

Chipotle, in an industry where many jobs are filled multiple times a year, says employee turnover at its restaurants nationwide has climbed to more than 125 percent a year since the investigation, from below 100 percent. In some markets, it says, managers report interviewing 30 to 40 candidates to fill one position, compared with 10 previously.

So now Moran, 45, is an outspoken advocate for changing immigration laws. In recent months, he has met with Sens. Michael Bennet and Mark Udall, both Colorado Democrats, and Charles Schumer, a New York Democrat, as well as Republican Reps. Darrell Issa of California and Lamar Smith of Texas. His message: Fix immigration.

“These guys need to know what is going on,” Moran said in his first major interview since the investigation. “Immigration is really messed up.”

While he isn’t prescribing a specific remedy, he has told lawmakers he needs access to a strong, legal workforce. A temporary guest-worker program might work in sectors such as agriculture, but it doesn’t address the needs for qualified labor on a year- round basis, he says.

By the end of the year, Chipotle expects to have added roughly 145 new outlets, with up to 165 added in 2012.

The chain views immigrants as critical to its success. About half of its 30,000 employees are Latinos, many of them store managers or in other leadership positions.