It might be bullying but, I suspect, it will be effective. The Tories, Labour and the Liberal Democrats ruling out Scotland sharing sterling after independence—as Nick Watt reported this morning — is designed to hole below the waterline the SNP's attempt to reassure voters that even after independence they could still share a currency union with the rest of the Union. (Alex Massie does a very good job of taking apart the SNP's response).
The potency of this argument is a reminder of what a disaster the Eurozone crisis has been for the SNP. It has made the Euro a far less attractive alternative currency than it was a decade ago and it has alerted everyone to the dangers of currency unions that aren't accompanied by political union.
That the Westminster parties are playing their ace card now, though, shows that they are not entirely confident about the result of the referendum.