Anyone can ask for anything, but fortunately you wouldn’t have to comply fully with this request.  (You wouldn’t be able to give out 80 years of the Form 990 even if you had them all because it apparently goes back only 78 years to tax years ending in 1941.)  If you have been filing the returns annually when due, you only have to provide forms for the last three years.  If you filed late or amended your return, you have to make copies available for three years after they were filed.

Regulations under Tax Code section 6104 generally require an organization that files a Form 990 (which includes (c)(4) social welfare organizations, (c)(6) trade associations, (c)(7) social clubs and a variety of others), Form 990-EZ or 990-PF to provide copies on the same day a person walks into the principal office of the organization to request them or within 30 days of a written request for copies.  You can avoid the delivery requirement by making exact copies available free on the organization’s website.  The organization can charge for copies so long as the charge is not greater than what the IRS charges per page. The maximum penalty for failure to comply is up to $10,000 for any one return.