Michael Smith shares his thoughts on Colin Kaepernick and explains that people should now focus on the substance of why Kaepernick is protesting in the first place instead of just focusing on Kaepernick. (1:13)

Michael Smith: Kaepernick 'is a man who is taking a stand for others' (1:13)

The Santa Clara police union has sent a letter to the San Francisco 49ers, warning that police might stop working the team's home games due to Colin Kaepernick's statements on police brutality and his wearing of socks during a practice that showed cartoon pigs dressed as police officers.

The letter, obtained by NBC Bay Area, states that if the 49ers do not discipline Kaepernick, "it could result in police officers choosing not to work at your facilities."

The letter also states that "the Santa Clara Police Officers' Association has a duty to protect its members and work to make all of their working environments free of harassing behavior."

It criticizes what it called anti-police statements made by Kaepernick, calling them "insulting, inaccurate and completely unsupported by any facts."

In another statement released Saturday, Chief Michael Sellers of the SCPOA said law enforcement officials have been "saddened and angered" by Kaepernick's stance, but plan to continue to do their jobs.

"[Kaepernick's] blanket statements disparaging the law enforcement profession are hurtful and do not help bring the country together," Saturday's statement said. "As distasteful as his actions are, these actions are protected by the Constitution. Police officers are here to protect the rights of every person, even if we disagree with their position. Police officers have sworn an oath to uphold the Constitution."

"I will urge the POA leadership to put the safety of our citizens first," Sellers said in the statement. "I will work with both sides to find a solution. In the meantime, I will ensure we continue to provide a safe environment at Levi's Stadium."

The 49ers reiterated Friday night that they stand behind Kaepernick and respect his right not to participate in celebrating the national anthem.

The Santa Clara police union issued a letter to the 49ers saying that officers might stop working the team's home games due to the controversy surrounding Colin Kaepernick. Chris Carlson/AP Photo

Kaepernick has become the focus of intense scrutiny for not standing during the playing of the national anthem in the 49ers' last two preseason games as a form of protesting racial injustice in the United States.

He also received criticism from the head of a national police association after he appeared on the 49ers' practice field wearing the socks.

Kaepernick vowed to continue to not stand during the national anthem until he is satisfied with the changes made toward ending racial oppression in the U.S., a position he reiterated after Thursday's game against the San Diego Chargers.

"Once again, I'm not anti-American," Kaepernick said. "I love America. I love people. That's why I'm doing this. I want to help make America better. I think having these conversations helps everybody have a better understanding of where everybody is coming from."

Kaepernick also said Thursday that he plans to donate $1 million to organizations that will help communities in need.

The 49ers had previously released a statement on Kaepernick's actions, saying, "In respecting such American principles as freedom of religion and freedom of expression, we recognize the right of an individual to choose to participate, or not, in our celebration of the national anthem."

Kaepernick is expected to discuss his actions on Sunday at a San Francisco church known for its activism on civil rights causes.

About 70 Santa Clara police officers work each 49ers game at Levi's Stadium, according to NBC Bay Area.

The union letter says Kaepernick's protest has "threatened our harmonious working relationship" with the 49ers.

The Associated Press contributed to this report.