Brooke Shields went inside Casa Bonita in Denver this week.
She used a false name to gain entry to the restaurant.
Shields pushed to approach Trey Parker and Matt Stone, the owners.
She wanted to raise reports from staff about unsafe conditions and inadequate pay.
Workers also cited health risks.
Employees say they met with backlash after talking about issues.
Following her visit, Shields shared support for the staff online.
She posted pages to their statements regarding the venue.