Pope Francis is arguably one of the most progressive pontiffs to ever lead the Catholic Church. He has taken controversial stances on many different issues, including abortion, climate change and same-sex marriage.

As a result, he may very well cause a stir when he speaks to the U.S. Congress later on this month, in spite of the fact that he was invited by Republican House Speaker John Boehner, notes Roll Call.

Back in June, the pontiff released an encyclical that linked the fight against climate change to the moral obligation of the Catholic Church to preserve humanity and help the poor. He dismissed climate change deniers and stated that the future of our planet is contingent upon the action that we take now.

Pope Francis also raised eyebrows when he recently commissioned priests to forgive women who have abortions, rather than excommunicating them from the church.

Meanwhile, a number of GOP members in Congress have been pushing to defund Planned Parenthood ever since a conservative anti-abortion group released videos that allegedly show medical workers affiliated with the pro-choice nonprofit discussing the sale of aborted fetal tissue. Other Republicans have even called for a government shutdown in order to defund Planned Parenthood, reported The Huffington Post.

Based on his prior actions, it is likely that Francis will not shy away from speaking about these issues when he addresses Congress on Sept. 24.

That means that he may very well scold lawmakers and supporters of corporate greed, emphasize our responsibility for stewardship of the earth, and even urge Congress to pass legislation on immigration reform, which he refers to as a "humanitarian emergency."

So far, the Vatican has already revealed the address will at least touch on immigration.