On Tuesday, Minnesota Gov. Mark Dayton signed a bill making same-sex marriage legal in the state.
The timing of the signing was not lost on San Francisco Archbishop Salvatore Cordileone, chair of the U.S. bishops' conference Subcommittee for the Promotion and Defense of Marriage.
"It is the height of irony that the Minnesota legislature decided, and the governor signed into law, the redefinition of marriage just after we celebrated the unique gifts of mothers and women on Mother's Day," he said in a statement  the bishops' conference released Wednesday.
"It is all the more so given the fact that in the last election Minnesotans were led to believe that there was no need to define marriage in the constitution, that nothing would change if the marriage amendment didn't pass," he said.
In the November elections, Minnesota voters rejected an amendment to the state constitution that would have defined marriage as between a man and a woman.
Cordileone went on to say the new law "renders senseless" the National Fatherhood Initiative of the Obama administration, since it claims "that a mother and a father together are superfluous and can be replaced by two men or two women." He added that sexual relationships outside of marriage are harmful to individuals as well as society.
"Instead of strengthening, the Minnesota legislature's decision to redefine marriage weakens motherhood and fatherhood, and so strikes a blow to all children who deserve both a mother and father," he said.
Minnesota's passage of the law makes it the 12th state to allow same-sex marriage  in the United States and the first in the Midwest to do so by legislative vote. Earlier in the month, legislatures in Rhode Island and Delaware also legalized same-sex marriage.
"There are many of us Americans, including many Minnesotans, who stand for the natural and true meaning of marriage. They know that men and women are important; their complementary difference matters, their union matters, and it matters to kids. Mothers and fathers are simply irreplaceable," Cordileone said.
"Instead of strengthening, the Minnesota legislature's decision to redefine marriage weakens motherhood and fatherhood, and so strikes a blow to all children who deserve both a mother and father," Cordileone said, calling on traditional marriage supporters to "redouble our prayers, efforts and witness."
"We know what it takes to work toward a culture of life even in the midst of laws that work against us. The same is true for rebuilding a culture of marriage. No matter what the horizon may bring, we will continue in charity and truth to stand for justice and for the most vulnerable among us," he said in the statement.