A railroad worker was crushed to death between two railcars over the weekend by a remote-controlled train in a CSX railyard in Ohio, raising concerns among unions about such technology.

The death highlights the need for an in-depth review of the use of remote-controlled locomotives, the Transportation Communications Union and Brotherhood of Railway Carmen said in a news release Sunday. Every major railroad has used such locomotives inside, and increasingly outside of, railyards across the country for years.

The National Transportation Safety Board is investigating the death, which happened shortly before 4 a.m. Sunday in Walbridge, Ohio.

Fred Anderson is the third carman killed in an incident involving a remote-controlled locomotive, the unions said.

“Enough is enough. A full-scale review of the use and practices around remote-control locomotives is long overdue. CSX — and every railroad — must evaluate their use of these supposed technological advancements to ensure they are actually making our members safer, and not merely replacing people to continue lining the pockets of Wall Street,” Transportation Communications Union National President Artie Maratea said in the news release.

CSX officials at the railroad’s headquarters in Jacksonville, Florida, didn’t immediately answer questions Monday about Anderson’s death.

The Federal Railroad Administration has approved the use of remote-controlled locomotives since 2005. They are primarily used inside railyards to help assemble trains. Regulators issued guidelines for railroads back then calling for precautions, including ensuring the trains don’t operate at speeds above 15 mph, but there aren’t detailed regulations on exactly how they can be used.

Typically, a railroad worker stationed on the ground near a train controls its movements with a remote, although sometimes that worker rides aboard the train while it is moving.

Railroad safety has been a key concern nationwide this year ever since a Norfolk Southern train derailed and caught fire in eastern Ohio in February. That crash prompted evacuations, lingering health concerns, a massive ongoing cleanup and calls for reforms.

CSX is one of the nation’s largest railroads, operating trains in 23 Eastern states and two Canadian provinces.