The speaker of the poem works in a factory, and he and his co-workers run when the border patrol shows up there, presumably to identify the majority of them as illegal immigrants and to deport them. The speaker claims that he is an American, but even his boss doesn't believe him and is complicit in his escape: he even gives him a dollar.
The structure of the poem implies that the border patrol itself is complicit, with the line "Their vans and my boss waved for us to run"—it is not the actual meaning of the line, but the line breaks are surely not an accident. The speaker implies that he really is an American citizen, but he runs anyway, "since I was on his time." His boss presumes that the speaker is an illegal immigrant, and since he is of Mexican origin and working with other illegal immigrants, it is probably best for him to run even if he is a legal citizen. The speaker imagines amazed crowds lining the streets, as though his run is not a run from the border patrol but a race, the kind of race that perhaps other cultures are encouraged to run, while Mexicans are encouraged to run from border patrol. Ironically, he shouts vivas—cheers—to American culture as he runs, but he is not completely ironic—he does truly love the opportunities that America represents.