EWTN Catholic Q&A

RE: Holy day of obligation
Question from Irene on 12-06-2012:

In your answer to Grace, you overlooked an important detail. When a holy day of obligation falls on a Saturday or a Monday, the obligation is usually lifted (Christmas is the exception). That is why her parish will not have a vigil Mass. Thank you for your great work here!

Answer by Catholic Answers on 12-06-2012:

Irene--

The USCCB's guidelines to the holy days of obligation in the U.S. state:

Whenever January 1, the solemnity of Mary, Mother of God, or August 15, the solemnity of the Assumption, or November 1, the solemnity of All Saints, falls on a Saturday or on a Monday, the precept to attend Mass is abrogated (source).

As you can see, Christmas is not the only exception. The Immaculate Conception is the patronal feast of the United States, and so the holy day obligation is not abrogated in the U.S. when this solemnity falls on a Saturday or Monday.