Ask when the cut affects structure, roof, rated wall, damper/access, grease/industrial duct, equipment, or another trade.
Watch out
Do not cut because the duct does not fit.
Check
Confirm the exact location from approved drawings and field marks.
Check what is above, below, behind, or inside the cut.
Verify whether the wall/deck/roof/shaft/beam is structural, rated, waterproofed, post-tensioned, or shared with other trades.
Steps
Confirm what you are cutting/drilling/fabricating.
Check latest drawing/shop detail.
Look for hidden utilities, structure, rated assemblies, roof membrane, or equipment parts.
Focus on the actual issue: not asking before modifying shop-fabricated piece.
Photograph or mark the condition if someone else needs to approve it.
Say this to your foreman
In Cutting, Holes, Penetrations & Field Fabrication, I'm looking at: Not asking before modifying shop-fabricated piece. What should I verify before I cut, drill, seal, cover, move, or install?