Brooke Shields went through Casa Bonita in Denver this week.
She used a fake name to enter the restaurant.
Shields pushed to talk to Trey Parker and Matt Stone, the proprietors.
She wanted to raise reports from staff about unsafe conditions and low pay.
Workers also cited health concerns.
Employees say they met with backlash after talking about concerns.
Following her visit, Shields shared support for the staff online.
She posted URLs to their statements concerning the eatery.