Will voluntarily cancelling a credit card adversely affect my credit rating?

One of the benefits of my job is a union-sponsored credit card, a Master Card. I have had this card for years and I enjoyed a decent interest rate. However, I just received a notice in the mail that the card was bought out by Capital One. On Fluther, I asked (coincidentally) about Capital One a few weeks ago, and I heard very negative things.

I want nothing to do with any credit card that is Capital One. I want to cancel the card right away. My current card balance is zero.

Will cancelling a credit card have an adverse affect on my credit?