Attempts to enforce immigration laws in the U.S. interior have proliferated in recent years, yet the effects of these laws on immigrants are largely unknown. This paper examines whether increases in immigration-related law enforcement since 2001 have adversely affected the labor market outcomes of low-education male immigrants from Latin America, a group that comprises the bulk of undocumented workers in the U.S. The crackdown on the use of fraudulent Social Security numbers, increased requirements for government-issued identification, and other changes associated with greater focus on national security likely lowered the demand for undocumented foreign-born workers in the years following the 9/11 terrorist attacks. Using Current Population Survey data and a difference-in-differences estimation technique, we find strong evidence of worse labor market outcomes among recent Latin American immigrants in the post-9/11 period relative to natives and prior Latin American immigrants. The results indicate a decline in employment, hours worked, and earnings among recent male Latin American immigrants relative to similarly low-skilled black and Hispanic natives and vis-à-vis Latin American immigrants who have been in the U.S. longer. Our findings are consistent with firms increasingly substituting legal workers for undocumented labor in the years following 9/11. © 2009 by the Association for Public Policy Analysis and Management.