The final version of a new code on university bosses' pay has been dubbed "woefully inadequate" by the main union representing university staff.
The voluntary code is published amid concerns about spiralling pay rises for senior staff and calls for restraint.
The Committee of University Chairs, which wrote the code, says it will mean a more transparent and open system.
But the University and College Union said "a bizarre gentleman's agreement" would not curb excessive pay.
The final version:
- bans vice-chancellors from being members of committees that decide their pay
- requires universities to justify senior staff salaries
- includes guidance on "fair and appropriate" pay for senior staff.
The code is voluntary - but institutions which choose not to adopt it must explain publicly how their alternative arrangements meet the principles of the guidance.
Each institution must publish yearly details of its vice-chancellor's pay, including how this salary compares with the median earnings of the whole of its workforce.
If the difference is significantly above average, the institution must explain why.
Perks like free housing and cars, bonuses, expenses and other allowances will be included in the calculations.
Value for money
CUC chairman Chris Sayers said the guidance would "balance the need for recruiting the best talent with the need to demonstrate value for money".
"We are confident the new code will promote more transparency and improve the public's understanding of confidence in how decisions around pay are made."
Universities Minister Sam Gyimah said he was particularly pleased about the ban on vice-chancellors sitting on committees which set their pay.
But the UCU says the code does not go far enough.
The union points out that vice-chancellors will still be able to attend meetings as long as they leave the room when own their pay is discussed.
In fact, the guidance suggests that university bosses should be invited to meetings to advise on the pay of other senior staff, including professors.
"It is very important that the head of institution is present at meetings to discuss these staff and ensure that the committee's decisions are well-informed," says the guidance.
UCU general secretary Sally Hunt said she found this "staggering".
"A bizarre gentleman's agreement where the boss steps outside while their pay is discussed is not how you tackle excessive pay.
"If university leaders are to be held properly accountable, we need students and staff to be sitting on the committees which set their pay," she added.
The Office for Students called the code's publication "a positive step" but said it was now time for vice-chancellors and university governing bodies to "show real leadership on this issue".
"While the code provides useful guidelines, tough questions need to be asked about high pay in the sector," said OfS chief executive Nicola Dandridge.
OfS will publish its own information requirements for higher education bosses' pay later this month and Ms Dandridge warned: "Where an institution breaches our regulatory conditions, we will not hesitate to intervene."