I would go with B.
Reason : When is used to indicate the period of time

pnk wrote:Source: OG Verbal

Request discussion between choice A & B:

In reference to the current hostility toward smoking, smokers frequently expressed anxiety that their prospects for being hired and promoted are being stunted by their habit.

(A) When referring to the current hostility toward smoking, smokers frequently express anxiety about
(B) Referring to the current hostility toward smoking, smokers frequently express anxiety that

The idiom "Anxiety about " and "Anxiety that " both are correct. So we can not distinguish between A and B on the basis of Idiom alone.

The use of WHEN in A needs a time reference and that is lacking in the modifying sentence after comma.

Also B is more concise when compared to A .

So I will go with B .