The general secretary of the University and College Union has pledged to continue to press private colleges on issues such as quality of provision and working conditions after claiming that the union had received "legal threats" for speaking out.
Sally Hunt was speaking before the UCU's annual congress in Harrogate this week, where she will announce her intention to stand for re-election later this year. She will also appeal for a debate over the UCU's future as it prepares to mark the fifth anniversary of its formation from a merger of two unions.
In an interview with Times Higher Education, Ms Hunt warned that recent changes could create a "two-tier" system split between elite universities for the rich and cheaper provision for poorer students.
In order to minimise the government's financial contribution to higher education, ministers will bring in a "whole sector of private provision", she said.
"We have been saying over and over again - sometimes with legal threats against us by some organisations - that we have issues about the quality of provision they will bring in and the type of education."
In a warning to private colleges, she added: "Those institutions should be more worried about us, because we won't allow the introduction of working conditions that undermine our current members or current provision."
Ms Hunt said that since the UCU had been formed, it had enjoyed a "steadily growing" membership and a higher public profile.
"Whether people have liked what we had to say or not, we've put the issue of post-16 education firmly in the spotlight," she added.
Asked if a merger with the National Union of Teachers was a possibility, she said: "My personal view is still that there should be one education union."
The idea is "still on the table", although "not a priority".
Her more immediate concerns include reducing the UCU's administrative spending and canvassing members' views on reducing the size of its national executive committee.
That will put Ms Hunt on a collision course with the UCU Left, which is already likely to field a candidate against her in the leadership election, which will start in the autumn.
One major issue facing the UCU is the future of the Universities Superannuation Scheme.
The employers recently won their battle to cut USS benefits, creating a two-tier split between current members on final-salary pensions and future members who will receive a much lower-value career average revalued earnings (Care) scheme.
The UCU, which represents all USS members through its official governance role in the scheme, has threatened to take "sustained" industrial action over the cuts.
Asked if the UCU had failed in its USS responsibilities, Ms Hunt said: "We would have failed if we hadn't tried our best to find a solution."
The union "pulled the employers back from some of their greatest excesses in terms of the proposals at the beginning of the process".
She also responded in bullish fashion to the suggestion that the UCU should have tried to reach a compromise on a good-value Care scheme from the outset, insisting it was "a myth that we have said 'only final salary'?".
She added: "Do I think it is all over? No - not by a long chalk."