Nine new fare inspectors began their field training on TriMet buses and MAX trains Monday, as Portland's regional transit agency beefs up its security in an attempt to stop transit riders from using the system without paying.

TriMet already employed three fare inspectors but added nine more. The Oregonian first reported the announcement Monday.

Rider fares account for 16 percent of TriMet's revenue.

TriMet spokeswoman Roberta Altstadt says these fare inspectors will double as health and safety security after a series of physical attacks on Portland city buses and trains.

Before today, TriMet enforced fare payments by relying on its existing staff working on rotation between fare inspection and other transit system jobs like coordinating extra transit service or helping with rider safety.

These new inspectors will also act as security on buses and trains, but fare enforcement "will be their primary job," according to a TriMet news release.

TriMet's new fare inspectors will team with customer safety officers and will be assigned to particular areas of the city. This way "they can get to know daily riders better and the riders can get to know them," Altstadt said in a statement.

Nearly every effort to increase security and fare enforcement on TriMet has been met with fierce backlash. Some riders and social justice advocates argue that fare checkers disproportionately target people of color—and the Bus Riders Union wants transit to be free.

But bus drivers and train operators—whose union has great sway with the agency—want more security, and other riders complain about scofflaws on TriMet. The agency's hirings, which don't include additional armed police, appear to aim for a middle ground.