In this study, we explored Turkish preservice teachers' (PTs) informal reasoning regarding COVID-19 vaccination and new media literacy (NML), and investigated potential relationships between their informal reasoning and NML levels. Participants of the study were 410 PTs enrolled in teacher education programs of 19 different universities in Turkiye. The New Media Literacy Scale was employed to determine PTs' NML levels, while four open-ended questions assessed the informal reasoning in terms of the quality, quantity, and diversity of the arguments. PTs mostly generated scientific and risk-oriented arguments, respectively, with a notable absence of ecological and economical-oriented arguments. PTs' highest quality arguments were in science and risk-oriented reasoning modes, while the lowest were in economy and ecology-oriented reasoning modes. Additionally, the study found a limited diversity in PTs' arguments. The quality, quantity, and diversity scores of supportive arguments were higher than those of counter-arguments and rebuttals. PTs exhibited moderately high NML, with the lowest mean score in critical prosumption. Furthermore, a weak but significant positive correlation was found between the quantity, quality, and diversity of PTs' arguments regarding COVID-19 vaccination and their NML levels, except for the correlation between the diversity of arguments and critical prosumption, To enhance PTs' critical prosumption levels, and facilitate their effective use of media in addressing socioscientific issues, teacher education programs can focus on developing PTs' NML specifically in the context of controversial topics through targeted courses.