In May 2019, during his campaign for state senate, Mastriano was accused of spreading Islamophobia after sharing several posts on his campaign Facebook page targeting Muslims. "Islam wants to kill gay rights, Judaism, Christianity and pacifism" read one of the posts, which critiqued the common "Coexist" bumper stickers. After the fire at the Notre-Dame cathedral in Paris, Mastriano had shared an image that was circulated implying that it had been an act perpetrated by Muslim terrorists, with a caption reading "something wicked comes this way". He also made birtherist allusions regarding president Obama.