Angus Robertson said STV was an important part of Scottish identity and culture and had a key role to play in Scottish broadcasting.
He said: “The sustainability of quality news from reliable sources is crucial in the fight against false or misleading information.
“It is alarming to see decisions to reduce services and resources of news provision across the country, particularly given STV’s public service commitments to invest in news and help tackle misinformation.”
Describing the plans as a “worrying step backwards”, the culture secretary said he would “continue to champion stronger journalism and a Scottish broadcasting sector”.
In a statement, STV chief executive Rufus Radcliffe said: “The way audiences consume news content is changing rapidly and fundamentally.
“Our output needs to respond to that as linear viewing declines and digital consumption of news increases.”