NUS UK president Amira Campbell said "students and academics overwhelmingly already believe that universities and students' unions know how to do freedom of speech, and there is already plenty of legislature around the issue".
"I am disappointed in the governing bodies who have prioritised this over protecting and supporting marginalised students," she added.
The guidance on the new law was issued after universities requested clarity from the OfS on how to best uphold freedom of speech, after the University of Sussex was fined £585,000 for failing to do so in March.
The university was issued with the fine earlier this year under existing powers, after the OfS said its policy on trans and non-binary equality had a "chilling effect" on freedom of speech.
Kathleen Stock had previously resigned from her post as philosophy professor at the university, following protests by students against her gender-critical views.
The university has begun a legal challenge against the fine, arguing that the investigation was flawed.
Universities UK, which represents 141 institutions, said at the time of the fine that it would write to the OfS to clarify what would represent a breach of freedom of speech rules.
They now say they are "pleased" the OfS has taken on feedback, and would "make sure universities are appropriately supported to comply" with the new rules.
From this summer, the new law will place a stronger responsibility on universities in England to uphold freedom of speech and academic freedom.
The OfS can sanction universities, with the potential for fines to run into millions of pounds, if they are found to have failed to do so.
Almost every aspect of university life - from protests to debates, training and teaching - is covered by the new guidelines on how the law will be applied.
For returning students, or those starting university this year, there may be not be a noticeable immediate change, but Dr Ahmed says the law is about the freedom for anything to be discussed or taught.
Speaking directly to students, the director for free speech said: "You should expect to face views you might find shocking or offensive, and you should be aware that's part of the process of education."
He added that students should be able to express any view, no matter how offensive it is to others, as long as it is not outside what is generally allowed by law, such as harassment or unlawful discrimination.
The Union of Jewish Students said it was pleased the guidelines said Holocaust denial was not a form of protected speech under the law, while also ensuring that universities will have to protect students against antisemitic harassment.