It is actually easier to provide a list for teas and herbs that are safe in pregnancy than list which ones to avoid! Below is a short list of common herbs to avoid throughout pregnancy, unless otherwise advised by a trained herbalist or naturopath. Keep in mind there are many other herbs that are not safe in pregnancy.
Licorice root (Glycyrrhiza glabra)
Laxative teas (senna, aloe, cascara, rhubarb)
Yarrow (Achillea millefolium)
Goldenseal (Hydrastis canadensis)
Fever Few (Tanacetum parthenium)
Juniper berries (Juniperus communis)
Black and green teas - the occasional cup of caffeinated tea is most likely going to be safe but try sticking to the decaffeinated forms due to their lower caffeine content, and avoid all together in the first trimester.