Tina Knowles signed and shared the letter, which is also endorsed by her daughter Solange Knowles, on social media over the weekend.
The missive is addressed to Senate Majority Leader Mitch McConnell as well as Minority Leader Chuck Schumer.
Octavia Spencer, Regina King, Jada Pinkett Smith, Whoopi Goldberg, Kerry Washington, Taraji P Henson, Gabrielle Union, and Janelle Monáe have also provided their signatures.
They are joined by Kelly Rowland, Michelle Williams, Lena Waithe, Rashida Jones, Tiffany Haddish, Yvette Nicole Brown, and more.
Relatives of George Floyd, Breonna Taylor, Eric Garner, Amadou Diallo, Trayvon Martin, Dontre Hamilton, Oscar Grant, Jordan Davis, and Sandra Bland are also listed as signatories.
The letter publicly supports the Health and Economic Recovery Omnibus Emergency Solutions (HEROES) Act, a $3 trillion coronavirus relief bill.
The bill, according to the letter, would provide a safety net “for those most impacted by Covid-19, including disproportionately impacted black and brown communities, through provision of healthcare, economic security, justice system reform, housing, and voting access”.
“In passing this legislation, you will take an affirmative step towards declaring that Black lives matter,” the letter adds. “You will help build an America as good as its ideal.”
The House of Representatives passed the bill in May.
It has been met with opposition from Republicans and is expected to be at the centre of future coronavirus relief negotiations.