One of the ways fibroid tumors (including leiomyomas, myomas, or fibroids) can cause infertility by blocking the fallopian tubes. (1st reference link)
The 2nd reference link is an article from Georgetown University Hospital. In this article, the author states that fibroids causing infertility and/or repeated miscarriage is a common myth and there is no scientific evidence supporting this.
3rd reference link - states fibroids may cause infertility in a number of ways including (1) blockage of fallopian tubes that prevent either the egg or sperm getting to proper location for conception, (2) a large fibroid may distort the pelvic anatomy sufficiently to make it difficult for the fallopian tube to capture an egg at the time of ovulation, (3) a fibroid can intrude into the uterine cavity creating a mechanical barrier to implementation, (4) fibroids in the muscle portion can cause an alteration of blood flow; (5) fibroids growing in the uterine cavity may act as a foreign body and can cause an inflammatory response that makes the uterine environment hostile for an embryo to implant.