There are groups within Christianity who believe that it is wrong for women to wear pants. Their belief is that pants are men's clothing and therefore a woman should not wear them.
Under the covenant God made with the Israelites (the Old Covenant), He instructed them not to dress in a manner that would confuse others as to one's sexuality. Men were to dress as men, and women, as women. As the Bible says: "A woman must not wear men's clothing, nor a man wear women's clothing, for the LORD your God detests anyone who does this."1
God's purpose in this was to maintain the distinction of the sexes. This, however, does not prohibit women from wearing women's slacks, or even pants that would normally be worn by a man. What this verse is saying is that we should not dress in such a way as to fool another into believing that we are of the opposite sex. A lady should dress as a lady would in her society, just as a man should dress as a man would in his society.