Beyoncé is "sick and tired" of young men and women of color being shot and killed by police.
"These robberies of lives make us feel helpless and hopeless but we have to believe that we are fighting for the rights of the next generation, for the next young men and women who believe in good," Beyoncé wrote.
Beyoncé was criticized earlier in the year for her song "Formation" and her subsequent halftime performance during the Super Bowl, which was described by some as anti-police.
The Lemonade singer is explicit that her letter isn't a slight towards all police officers, rather it's aimed at any officer who "fails to value life" and "believes that murder or any violent action by those who are sworn to protect us should consistently go unpunished."
The letter calls on fans to contact their local representatives to demand political, social and judicial change.
The death's of both Sterling and Castile sent shock waves throughout the country this week. The shooting of Sterling was captured on video and Castile's girlfriend broadcast his killing's aftermath on Facebook Live.
President Obama said earlier Thursday that “all Americans should be deeply troubled” by the shootings.