A "hostile" wind is picking up strength across America, threatening to sweep traditional moral beliefs.

U.S. Supreme Court Justice Samuel Alito issued the warning last week while addressing a group of Catholic lawyers in New Jersey, the Associated Press reported.

Alito said the nation's commitment to religious liberty is being tested by those who oppose traditional values.

He recalled that when he made his dissent in the Supreme Court's landmark same-sex marriage ruling in June 2015, he predicted that those who would oppose the decision would be vilified and treated as bigots.

He said this is happening now. "You don't need a weatherman to know which way the wind blows," Alito said, quoting the lyrics of a Bob Dylan song. "A wind is picking up that is hostile to those with traditional moral beliefs."

Alito sees darker days ahead over the issue of religious liberty. "We are likely to see pitched battles in courts and Congress, state legislatures and town halls. But the most important fight is for the hearts and minds of our fellow Americans," he said. "It is up to all of us to evangelize our fellow Americans about the issue of religious freedom."

This was not the first time that Alito issued a warning on the "greater danger" facing the constitutional principle of religious freedom in America.

In November last year, in an address at the Federalist Society's 2016 National Lawyers Convention, he warned that America's constitutional structure is facing "unprecedented challenges."

He spoke about the threats currently facing constitutional rights such as religious freedom and free speech.

He likewise quoted a line from a Dylan song—"It's not dark yet, but it's getting there"—to underscore the threat on religious liberty.

The warning on the threats facing religious liberty and free speech was sounded as early as October 2012 when the Heritage Foundation issued a statement noting that "all across America, religious institutions and individuals are being subjected to increasing restrictions on their free exercise of religion and freedom of speech."

Written by Jay Alan Sekulow, Heritage Senior Research Fellow, the statement said the "crackdown" can be seen in various sectors. For instance, it cited "employers or health care professionals being required to provide or facilitate abortions against the dictates of their faith."

"This rising disregard for religious liberty represents a marked break from the long-standing American tradition of accommodating religious practice and expression that predates the ratification of the Constitution," it said.