Authorities say Michelle Carbajal, 38, pleaded guilty to 21 felony counts of altering public documents and 21 felony counts of computer access and fraud.
The investigation began when Carbajal's supervisor became suspicious and reported her.
Officials found that Carbajal took more than $23,000 total from 14 people to mark that they had passed both the written and driving tests to obtain a commercial license between 2008 and 2010, prosecutors said. The individuals were referred to her through a third party.
"Carbajal's actions endangered public safety, as some of these tests were safety-related including proper use of specialized brakes, proper pulling of double trailers, the ability to drive semi-trucks and other commercial vehicles, among other skills," the D.A.'s office said in a statement.
She is expected to be sentenced to four years when she is sentenced on June 6.