Interviewed by the nature magazine Suomen Luonto on Monday, Niinistö said intervention might take the form of a threat of fines or even a suspension of operations. Local environmental officials in the northern Savo region say sulphide levels near the mine have once again begun to rise.
The Finnish Food Safety Authority (Evira) says it will investigate recent bird deaths at the mine later this week.
Last Thursday dozens of dead birds were washed up in a processing pool at the mine. Talvivaara says it is examining how such deaths can be avoided in the future. Company employees are also making efforts to remove birds that find their way into the mine.
Reputation on the line
The Talvivaara mine currently produces nickel and cobalt, and plans to begin producing uranium. It has been frequently accused of polluting the surrounding area.
By the end of last week, some 160 complaints and comments had been filed regarding the planned expansion of the mine's operations. In mid-April, the municipality demanded that the Talvivaara company to pay more attention to the views of nearby residents and those who own holiday homes in the nearby Vuokatti resort area.
In March high levels of hydrogen sulphide were apparently responsible for the death of a worker at the mine. The incident led to a temporary closure of the facility.