Hi, I work for an accounting firm in New York. Myself and several other employees have a question if any of you can answer regarding OT, since we are heading into tax season where OT is required to be worked.

During normal season we work 37.5 hours a week, our salary is based on working this amount per week. During busy season we are expected to work 50+ hours a week, overtime is paid after 40 hours at straight time, however we are not paid for the hours worked between 37.5 and 40 hours, which comes to 2.5 hours per week. So basically we have to work 2.5 hours for free every week for about 10 weeks. Is this legal? Thanks.

It might be. I'm assuming you are nonexempt because you are getting overtime pay when you work over 40 hours.
http://www.dol.gov/dol/allcfr/ESA/Title_29/Part_778/29CFR778.114.htm

What happens when you work less than 37.5 hours in a workweek? Is your "salary" docked?

If we work less then 37.5 and we do not make up the time we are docked the pay from our check. Thanks alot for answering. From reading the DOL law it sounds like if time is docked for not making the 37.5, then what my employer is doing is not legal. Thanks again for answering.

That is my understanding of the regulation as well.