There is nothing in scripture that says oral sex is wrong. My husband and I both practice it, and I love it; receiving AND giving. Your husband shouldn't pressure you into oral sex if you are uncomfortable with it.
However, I think John posed a very good point. Also, many women use the "you shouldn't pressure me" as an excuse to deny their husbands. While he shouldn't pressure you if you aren't comfortable with it, you should also recognize that it is important to him. I think often times women feel that, because their husbands want sex a lot or like certain aspects of sex, that the wife may not be comfortable with, the wives suddenly think their husband is being insensitive. When it's not that at ALL.
I would recommend you do the things John suggested, as well as TALK to your husband about this. Do NOT argue. It will be difficult, but men often feel rejected by their wives when they argue about sex. Sex is very important in marriage, and is meant to be enjoyed by BOTH partners. You and him. However, if he knew exactly how you felt, without him feeling like he was wrong for ANYTHING(because, seriously, he shouldn't feel like he's breaking the marriage over this. Threatening to leave him is wrong, imo.), it might make things better. Communication without condemnation is needed here.
Again, should he pressure you? No. Should you threaten to leave him? No. I'm not saying you should just give him oral sex. My own experience, I wasn't too keen on it either. However, when I opened my mind and saw how much he enjoyed it, and how happy it made him, it made me exceedingly happy to know I could please him that much. And then, ya know what? He started doing the romantic things I'd been aching for. Sacrifices are rewarded. Just some food for thought.