Washington (CNN) -- Lenient enforcement of a law requiring U.S. citizens to have passports when re-entering the country at land border crossings has heightened the risk that an imposter might get in, according to a government report released Monday. Under the law, which took effect in June 2009, U.S. citizens must show passports or some other authorized travel documents like a military ID when returning to the United States. Those who don't are supposed to undergo further screening to confirm their citizenship. But, during a phase-in period that now has stretched over 18 months, very few travelers have been referred to secondary screening, the report from the Homeland Security department's inspector general's office found. That assertion -- the study concluded -- "increases the risk that someone could enter the U.S. under false pretense of citizenship."
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A Homeland Security department IG report looks at enforcement of a new passport law
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The study finds that many people get in the U.S., by land, without required documents
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Compliance rates are much higher along the Canadian border than the Mexican one
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The border patrol agency says its phased-in compliance effort is working
On a typical day, some 700,000 people arrive at @placeholder land borders, trying to get into the country.