You might ask the manager or owner, if they make sure their workers are legal with e-verify. It will help word to get around that Americans are becoming concerned about illegal workers. A lot could be accomplished, if even a fraction of Americans would avoid using businesses that hire illegals and let the management know that you only want to support businesses, which hire legal American workers. Losing a few percent of their customers can be critical to a business.
There is a Chicano nationalist movement in the US, which teaches that the Southwestern United States (Atzlan) was stolen and belongs to the Mexicans. This movement advocates a separatist agenda for the Southwest and a return of the region to Mexico. One of their goals is to promote illegal migration of Latin Americans to the United States in order to further this anti-American, separatist agenda and eventually control the entire Southwest. Consumers should not encourage and feed this agenda by supporting businesses, who employ illegal aliens.
Those, who come to America illegally, should never be rewarded with citizenship for breaking the immigration law. That only undermines the sovereignty of the United States.
This is also an indirect way of sending Congress a signal that you want them to enforce the immigration laws that are already on the books. It is neither illegal nor immoral to withdraw support for businesses, who are exploiting illegal aliens.