In an article for the Globe and Mail style section, Amy Verner discusses the inappropriateness of going braless or wearing tops that show bra straps in an office environment. Verner's article basically points out that going braless can result in embarassing and unwanted attention, and offers advice on covering up and finding alternatives to the standard bra (camisoles, nipple covers, etc.).
The article is part of an ongoing column called Suitable, and it drew the most attention of any article in the series to date with 143 comments posted by readers in response. My quick perusal of the comments that were posted puzzled and disappointed me. Most of the contributors interpreted going braless in the office as a freedom of expression issue ("Women should be able to dress their own bodies however they want") and railed against conservatism and prudishness, complaining about the hypocrisy of oversexualizing female bodies yet asking women to cover up in the workplace.
In my opinion, these readers missed the point entirely. Wearing a bra to work is not a negation of self-expression or a suppression of female empowerment; it's more like an expression of workplace etiquette in the way it complies to an accepted dress code. Office attire evolved as a way of defining appropriate, inoffensive clothing to wear in a close space where you come into contact with different personalities daily. In any office setting, there are people with various religions, political viewpoints, and aesthetic sensibilities; some individuals may have more conservative views and feel really uncomfortable with a coworker who goes braless or wears cleavage-baring tops. By adhering to a dress code and erring on the side of more conservative dress (or in this case, wearing a bra), employees show they are making an effort to make their coworkers feel more at ease.
That being said, I work in an office environment that has no dress code and often sees employees come to work in jeans and sneakers. I myself am grateful that I can dress up or dress down depending on how I feel, and that I don't have to don a suit and pantyhose or cram my feet into high heels every day. In this context, wearing a strappy tank top that shows bra straps is not a big deal when compared to doing the same in a workplace where suits are the norm. However, even with such a lenient dress code, there are still some unspoken "common sense" rules almost everybody adheres to, including wearing a bra and not wearing anything too revealing.