San Francisco Archbishop Salvatore Cordileone said Monday he would speak at an upcoming rally sponsored by the National Organization for Marriage (NOM) and other groups opposed to marriage equality.

Cordileone said it was his duty to declare the truth “about the human person and God's will for our flourishing. I must do that in season and out of season, even when truths that it is my duty to uphold and teach are unpopular, including especially the truth about marriage as the conjugal union of husband and wife. That is what I will be doing on June 19.”

Dozens of California leaders, including House Minority Leader Nancy Pelosi, who represents San Francisco, and California Lt. Gov. Gavin Newsom, had asked Cordileone to skip Thursday's rally and march to the steps of the Supreme Court. Headlining NOM's second annual March for Marriage will be former presidential candidates Rick Santorum and Mike Huckabee.

“While we may disagree on the subject of marriage equality, we do agree that every person is a child of God, possessed of the spark of divinity and worthy of respect,” wrote Pelosi, one of the country's most powerful Catholics.

(Related: Nancy Pelosi calls NOM's anti-gay marriage march “venom masquerading as virtue.”)

Cordileone defended his participation in the event.

“The March for Marriage is not 'anti-LGBT' (as some have described it); it is not anti-anyone or anti-anything,” he wrote. “Rather, it is a pro-marriage March. The latter does not imply the former.”

“Please do not make judgments based on stereotypes, media images and comments taken out of context,” he added. “Rather, get to know us first as fellow human beings”

In 2008, Cordileone played a critical role in getting Proposition 8 on the ballot. The NOM-backed constitutional amendment was a response to a California Supreme Court ruling striking down the state's ban on same-sex marriage. Proposition 8, which re-instituted a marriage ban, was struck down as unconstitutional last year. Most recently, he said he supports an amendment to the U.S. Constitution limiting marriage to heterosexual couples.