"It is not only Sandstrom, but what the LDS Church's response to this is and their people carrying the bills," he said. "Most of the representatives belong to that church and most of the bills that are introduced in the Capitol go against human rights. We think the church has a responsibility to speak out against it publicly."
Sandstrom, the Orem Republican who is carrying HB70, said Saturday he thinks it "highly improper" for a person to ask a foreign government to interfere in the internal matters of Utah.
He also said Lopez-Vargas shouldn't put the church in that position.
"It's unfortunate that someone would try to blackmail the LDS Church," he said.
The church did support the principles of The Utah Compact, a document whose supporters say is a compassionate approach to immigration reform and one that has largely been cited by those who oppose Sandstrom's measure. But the church also did not officially sign the compact and instead issued a statement simply supporting its principles.
Sandstrom has also said he supports the principles of the compact, though he points out that the compact doesn't use the word "illegal" when talking about immigrants.
When the compact came out, Sandstrom said he took it as the church taking a shot at his bill.
Church officials on Saturday did not comment on the Lopez-Vargas letter and referred inquiries back to its statement on the compact.
Tony Yapias, director of Proyecto Latino de Utah, said the church should not take the actions of Lopez-Vargas lightly but also said he wasn't sure it is the best approach in the debate.
"I don't necessarily like the approach of using missionaries to negotiate immigration matters," Yapias said. "But given that, I can see there is a lot of frustration in the Latino community from LDS Latinos primarily about the church not taking a stronger position on the matter."
Lopez-Vargas, who has dual citizenship and makes regular trips between the United States and Mexico, said he is acting as an individual. But Yapias said Lopez-Vargas has legitimate links "at the highest levels" in the Mexican government.
But Ignacio M. Garcia, a history professor at Brigham Young University, said the Mexican government also has strong ties to the Mormon Church and he doubted Lopez-Vargas could change the policy between two large entities.
He also said the action is likely born of frustration with the church, which, he said has been perceived to have not taken enough action in the immigration debate. Still, he had a hard time seeing much success with the Lopez-Vargas approach.
"The church has cultivated a very good relationship with the last administration [of President Vicente Fox] and it's not been different with President Calderón," Garcia said.
Lopez-Vargas plans to deliver the copy of the signed letter to the Mexican consulate Monday morning.