Millions of immigrants stand to benefit from President Barack Obama’s executive order on immigration, but there will be “significant challenges” to implementing it, according to a top administration official speaking at the Los Angeles Convention Center.

“The first is that we need people to know that these programs exist,” said U.S. Citizenship and Immigration Services director Leon Gutierrez, speaking on Monday at the the site of a weekend workshop  that drew more than 1,300 immigrants seeking details on the new immigration plan.

Obama's executive order could allow as many as five million immigrants to obtain temporary relief from deportation and work permits, among them parents of U.S. citizens who have spent more than five years in the country and immigrants who arrived as minors.

“While it is thrilling that we had the lines out there yesterday of people ready to go, wanting to get advice, wanting to know what documents they need to assemble, there are still many who do not know about these important programs,” Gutierrez said.

Gutierrez called on the audience, which included immigrant advocates and service providers, to help spread the message to potential applicants. Those eligible will need to gather documents to prove how long they have lived in the United States, among other things.

He also praised efforts in Los Angeles and elsewhere to combat the inevitable scams that prey on hopeful immigrants.

But Gutierrez provided little additional details on how and when the program will be implemented. Last week, he told Spanish-speaking reporters that immigrants eligible for deportation relief and work permits could begin applying in February and May, starting with people who arrived in the U.S. as minors and followed by parents of U.S. citizens who have lived in the U.S. more than five years.

Obama’s executive order also called on the agency to expand payment options for people struggling to pay the steep fees required to apply for U.S. citizenship.

“For the first time, we’ll be offering credit card processing for naturalization applications,” Gutierrez said. “This should come in the next few months.”

While there will be no fee waiver, Gutierrez said that the agency – which is funded by the fees it charges - would be looking into other “innovative financing techniques”  for immigrants to pay application costs.