According to Victor Herbert [1994, p. 1215S], iron deficiency is twice as common in vegetarians as in omnivores. Other sources claim that this is not the case, but it's nevertheless interesting to read that "Prolonged iron deficiency damages the gastric mucosa and promotes atrophic gastritis and gastric atrophy, including loss of gastric acid and I.F. [intrinsic factor] secretion, and therefore diminished vitamin B-12 absorption."

We know that getting enough iron on a vegan diet is not a problem (but nobody is guaranteed that it won't happen; just like meat eaters we need to get the iron from somewhere. Anyway, Victor Herbert, who made so many attempts on making veganism appear as unhealthy, simply tried too hard, because statements from his various attempts to harm the vegan movement contradict each other.

Herbert conclusion to what I quoted above, is "This would cause vitamin B-12 deficiency in twice as many vegetarians as omnivores". I think he is wrong, because there are so many other reasons that vegans will become B12 deficient other than his theory about iron. Still, if iron deficiency can lead to B12 deficiency, it's more important for vegans to monitor their iron levels than it is for others.

Here are some links which are useful if you look for vegan iron sources: