Cristina Bustos told the Palm Beach Post the package has the birth certificates of two relatives also living in Florida who need them to apply for passports. She was told the package would remain at a UPS center in Louisville, Ky., until she sends a copy of her green card.

Bustos said she believes the demand is unfair and told the UPS representative so.

"She represents a private company," she said. "She's not an agent for the immigration service, and I have no obligation to show her my immigration status. We paid to have those documents sent, and they should deliver them to us. There is nothing illegal in that envelope."

Kirsten Petrella, a UPS spokeswoman, said the company is obliged to follow directives from Immigration and Customs Enforcement. The agency believes documents like birth certificates are sensitive because they could be used by terrorists to get false documents, she said.