Apparently there are three major divisions of the Lutheran denomination: ELCA, LCMS, and WELS. WELS is the acronym for the Wisconsin Evangelical Lutheran Synod. From what I have read, it seems to be the most conservative of the three.
WELS, characterized as theologically conservative, is the third largest Lutheran church body in America. With national offices today at 2929 N. Mayfair Rd., Milwaukee, Wis., WELS began in 1850 when three German pastors met in Milwaukee. Today, it has grown to over 1,200 congregations in North America. It has over 400,000 baptized members, which includes over 300,000 communicants, served by over 1,000 pastors.
During its history, WELS has taken a stand for what they believe. In 1961, they separated from the LCMS because of what they believed to be error in doctrine and practice. Of interest is their explanation of that withdrawal of fellowship between the WELS and LCMS.
Since 1872, when this confessionally sound federation of Lutheran synods was founded, the member synods were fully agreed on the fellowship principles that had brought them together. All held that complete confessional unity is the necessary scriptural basis for all practice of church fellowship, that is, for pulpit, altar, and prayer fellowship.
… In 1960, the Missouri men submitted their “Theology of Fellowship” to the Joint Union Committees. On the crucial point noted above, this document spoke of a “growing edge of fellowship” and contended that “in reaching out to those not yet in confessional fellowship with us there is the possibility of the beginning of the practice of fellowship.” This was the start of what has become Missouri’s position on “levels of fellowship.” In the meetings in May 1960, after three days of discussions, the Wisconsin delegation recognized that the consideration of this subject had reached an impasse.
The doctrine of church fellowship became the primary divisive issue that resulted in the 1961 Wisconsin Synod resolution suspending fellowship with the Missouri Synod. The resolution recognized the “Theses on Church Fellowship” [link] as “an expression of the scriptural principles on which the Wisconsin Evangelical Lutheran Synod has stood and which have guided it in its practice for many years.” Since their appearance the theses have been and are still recognized as such.
I don’t know enough about the WELS or LCMS to consider either a fundamentalist Lutheran denomination. And I would certainly disagree with the practice of infant baptism as described in this and other Q&A. But it is interesting to read about their willingness to defend and separate from those not holding to what they consider sound doctrine.