Tabloid Expressen's sources say Gustav Kasselstrand is one of the loudest voices within the party in favour of voting for the opposition centre-right Alliance shadow budget, and thereby causing a major parliamentary headache for Social Democrat Prime Minister Stefan Löfven.
Speaking to Swedish Radio News, Kasselstrand says: "We should play hard-ball now the Social Democrats and conservative Moderates have declared they don't want to talk with us, or negotiate with us."
However, Kasselstrand and the party leadership have not always seen eye-to-eye on many issues, news agency TT reports.
The Sweden Democrats will announce Tuesday afternoon how they plan to vote in the budget votes on Wednesday. If they choose to vote for the Alliance shadow budget, rather than abstaining or voting for the government budget, it could lead to the Löfven government's collapse, and possibly new elections early next year.