Originally Posted by
jbchybridrider
I think I've read there's rules against them, could be wrong though!
UCI rules would prohibit flat bars in a mass start road race because they require use of handlebars traditional to the discipline.
UCI rules don't apply to most racing in the US however.
USA Cycling rules don't appear to prohibit flat bars. The ends need to be plugged, there cannot be a forward extension or and elbow rest. Other than that, there does not appear in a quick review any rule against flat bars.
That said, I could have overlooked something, and I wouldn't bet that the USA cycling ref won't pull you at the start of your local crit.