Federal immigration agents arrested more than 100 workers Thursday at a Wal-Mart distribution center under construction in eastern Pennsylvania, authorities said.

The workers were detained on suspected immigration violations and loaded onto buses to be taken to Immigration and Customs Enforcement detention centers for processing, Department of Homeland Security spokesman Marc Raimondi said.

More than 50 federal immigration agents, joined by the U.S. Labor Department, Social Security Administration and state police, raided the construction site at the High Ridge Business Park, about 80 miles northwest of Philadelphia.

Wal-Mart spokesman Marty Heires said the detained workers were not employed by Wal-Mart but by subcontractors.

"Consistent with our corporate practice, we have written contracts with these subcontractors requiring that they follow all applicable local, state and federal employment laws," he said in a statement. "We will cooperate fully with U.S. Immigration and Customs Enforcement and the U.S. attorney's office in this matter."

The construction site is near Interstate 81, just northwest of Pottsville.

Schuylkill County Sheriff Frank McAndrew said at least 120 illegal immigrants, most of them from Mexico, were detained. That number was far more than ICE - formerly the Immigration and Naturalization Service - had anticipated, because the agency arrived with only one bus. McAndrew arranged for two more buses, which he said took the workers to Philadelphia for processing.

The sheriff said he began investigating the site more than two months ago after getting complaints from local tradespeople that illegal immigrants were working there, and he contacted federal immigration agents after verifying their allegations.

"You've got a situation here where illegal immigrants are coming into Schuylkill County and taking (local union workers') jobs for eight bucks an hour. They are working for poverty wages, and creating unemployment because our skilled tradesmen are out of work," McAndrew said.

Last month, Wal-Mart shut down work on seven stores under construction in North Dakota to check for illegal aliens after two illegal immigrants working on Wal-Mart projects in Bismarck were charged with molesting two 13-year-old girls. Charges against one of the suspects were dropped after authorities found out he was a juvenile.