Rebalancing 401(k) - tax consequences?

My employer matches my 401(k) contributions with company stock. Although this stock has been performing well lately, it has become a larger percentage of my 401(k) portfolio than I am comfortable with. (about 42%) I would like to transfer some of this stock into other mutual funds available to me in the plan. Will this cause any tax consequenses or anything like that? (I know there may be trading fees or other fees adminstered by the plan administration, but I'm concerned with ';hidden'; fees or expenses that may not be obvious.)