I sure you can legally refuse your company's request for your tax return or any part thereof. what makes me very suspicious is their asking for a form that would only be used by paid preparers. if you didn't use any software and mailed in your return, what could you provide them to prove you filed.
they should have all the info they need your W-2 and their books and records. say you paid your health insurance personally but didn't itemize. the only thing that would be left is your insurance invoices and checks.
personally I consider what they're asking to be an invasion of privacy. note I am not a lawyer. .
