HONOLULU -- Federal prosecutors on Friday said illegal immigration has become a threat to Hawaii's economy as they announced recent enforcement actions at local jobsites that led to 120 arrests with more to come.

"I am deeply troubled when I see deliberate violations of federal laws to take our jobs," Hawaii U.S. Attorney Ed Kubo said.

Hawaii's U.S. attorney displayed pictures of 23 men facing prison and deportation after being caught with fake documents they used to get work at a Kunia farm. He also reported arrests of 28 construction workers at the Honua Kai Resort on Maui.

There have been 120 worksite arrests since December, many apparently working an underground labor circuit.

"(They are) being brought to Hawaii to work for specific time periods and then being taken back to the mainland," Kubo said.

"We have seen a pattern of individuals coming in groups to work on certain projects and certain jobs, whether in agricultural, construction or even the restaurant industry," Immigration and Customs Enforcement Agent In Charge Wayne Wills said.

Investigators said they are still looking for evidence that the employers knew or should have known they were hiring so many illegals. They said the excuse that the workers had very good fake IDs may not protect the companies from civil or criminal penalties.

"If you are knowingly hiring illegal aliens, you better keep looking over your shoulder, because we are coming," Kubo said.

Employers can avoid trouble by calling ICE with their suspicions, agents said.

"If you just don't have that feeling that the document is genuine, then reach out to us," Wills said.

Authorities said they are throwing resources to the problem because it is getting worse, while at the same time jobs for legal workers are more precious than ever.