Simplify the following text for a Grade 15 native English-speaking person.
Original: After months he became highly critical of the involvement of ConfederaciÃ n Nacional del Trabajo ( CNT ) members in the Popular Front government , and he sent a letter to Federica Montseny ( Anarchist minister for Healt in the government against fascism ) .
Simplified: He became highly critical of the involvement of ConfederaciÃ n Nacional del Trabajo ( CNT ) members in the Popular Front government , expressing his views in an open letter to Federica Montseny ( Anarchist minister for Health ) .