>>I thought they only required quarterly is you were in business for yourself.<<
They will also require it of people who chronically “underpay.” If you owe over a certain threshold (I just don’t remember if it is a fixed dollar amount or a %) over several years, the IRS will require quarterly payments in addition to standard withdrawals. Essentially they make you pay to the level you “should have” if your pay cycle tax deductions are lower than their calculations.
Underpayment Penalties
You'll have to pay an underpayment penalty for 2009 if you owe more than $1,000 in taxes (after taking withholding into account) and:
Your taxes withheld don't cover at least 90% of your 2009 tax liability, or
Your taxes withheld aren't at least 100% of your 2008 tax liability if your AGI is up to $150,000 or 110% if your AGI is more than $150,000. (The amount is $75,000 if you're maried filing separately.)
AAArgh! what a bunch of garbledy gook! I don't understand.