Selling expired food is a violation of the law. Selling expired food is, in fact, a violation of the law.selling expired food is a fact of violation of law
It may be correct in the right context. Without a context, people wouldn't know what an "illegal fact" is supposed to mean. BTW, we still don't have the context (上下文) where 违法事实 is used. If your question is only about English and has nothing to do with Chinese, then you'll be better served by going to the English-Only forum.I wonder whether "illegal fact" is a correct term.
Presently the government agency is still conducting its investigation. Before the investigation reaches a conclusion, our company will not admit to any violation of the law.目前政府部门正在开展调查，在调查结果出来之前，我公司不会承认任何违法事实
I agree. A spokesperson of a company speaking from the first-person perspective (i.e., 我公司) is expected to avoid any suggestion that links 违法 with 事实.我感觉这句本身就有问题：既然我们否认，怎么还能叫“事实”？我会说“我公司不会承认任何违法指控”。
Legally speaking, 事实 does not mean 事情的真實情形. It could mean "a matter subject to investigation by the authority to establish whether a crime has been perpetrated", for instance, 中国证监会《结案通知书》: 经审理，你公司涉案违法事实不成立，我会决定本案结案 (http://szsb.sznews.com/html/2015-02/09/content_3146024.htm). Note that it is 你公司, not 我公司. 违法事实 refers to allegations of law violation.“违法事实”也是属于这一类的，是说关于违法行为的事实