When your business mails out 1099-MISC forms at the end of the tax year, you don't send them to corporations. Sole proprietorships and partnerships have to get a 1099 whenever they do $600 or more work for your firm, but corporations don't. Legal firms, however, are an exception to the rule.
Any attorney who does work for you worth $600 or more gets a 1099-MISC. You send a duplicate copy to the IRS as well. This applies regardless of whether the law office's business structure is a corporation, a partnership or any other type. What matters is the total for the year: you send your lawyers a 1099 whether they had, say, one $600 job or six $100 assignments. Lesser amounts are still taxable income, but you don't have to send out the form -- it's the lawyer's job to keep track.
You also send out a 1099 if you pay a corporation $600 or more in "gross proceeds" in a given year. That applies, for example, if someone sues your company and you eventually pay the plaintiff's attorneys a settlement. You don't have to know how big a fee the law firm collects, just that it's coming out of the settlement. You report fees to your lawyers in Box 7 of the form, gross proceeds in Box 14.
You need the firm's taxpayer identification number to report their income on a 1099-MISC. If the firm has done work for you in the past, you may have the information in your files. If not, you can request it by sending the corporation a W-9 form. The law says the firm has to provide you with its TIN after it gets the form. Unlike other W-9 recipients, it doesn't have to certify the number.
Don't dawdle with regard to sending out your 1099s. You should have a copy filed with the IRS by January 31, and you should have sent one to the legal firm by that date too. You do not send them to any attorneys you work with on a personal basis, such as the legal firm that handles your pre-nup or your estate planning. You only send 1099s for business expenses, so no matter how much your pay your personal lawyers, there's no form needed.
