Staff at Chicago’s Museum of Contemporary Art announced plans to unionize Wednesday, becoming the latest workforce to launch a union campaign at a major Chicago cultural institution in recent years. In an open letter signed by 32 staff members —about a third of union-eligible workers at the museum — employees said they were seeking wages that kept pace with inflation and Chicago’s cost of living, guarantees that benefits including sick leave and paid time off will not be decreased and will be expanded when possible, protections from layoffs and transparency around compensation. The staff membe…