antisabbatarian

from The Century Dictionary.

• noun One who denies the perpetual obligation of the sabbath law, maintaining that it was part of the ceremonial, not of the moral law, and was abolished by Christ; hence, one who opposes strictness in the observance of the sabbath: the opposite of sabbatarian. See sabbatarian, sabbath.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Eccl.) One of a sect which opposes the observance of the Christian Sabbath.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun One who opposes the observance of the Christian Sabbath.