UP and Slip-on Boots

For U.P> can the workboots be slip on boots?

I'm sure UP has the same requirements, but here is what is listed in the BNSF Safety Rules :

Safety boots must meet the following criteria
-Leather or leather-like upper
-Sturdy non-leather sole that will resist puncture
-3/8 inch to 1-inch defined instep.
-Rounded toe
-Above ankle (5-inch height as measured from inside boot)
-Minimum ANSI Z41.1 -- 75 pound impact and compression class toe.
-Chemical resistant
-Lace-up