Some lecturers and support staff at Queen's, Ulster Uni, and the Open University have started strike action over pay and pension disputes.
Members of the University and College Union also took to the picket lines on Thursday morning to protest over working conditions.
It marks the beginning of 14 days of strike action at 74 universities across the UK.
It's the second industrial action taken during this academic year.
Both Queen's and Ulster University will remain open and are working to limit the impact on students.
Queen's University says interventions are being implemented on a school-by-school basis.
In a statement it also said it expected many students would not be affected by the strike action.
A spokesperson said: “As with the previous round of action, this is primarily a national dispute that the University cannot resolve unilaterally.
“Positive discussions are ongoing at a national level to resolve the dispute with progress being made.”
A spokesperson for Ulster University said: “Whist strike action can be unsettling for our students; they can be reassured that we are taking steps to ensure that any whose studies may be affected by the strike are not disadvantaged at the point of assessment.
“We continue to work closely with staff and our Students’ Union to do everything possible to safeguard both the student and staff experience during this time.”
A spokesperson for Queen's University said they fully respect staff's right to take industrial action.
Likewise, an Ulster University spokesperson said they recognise that staff have not taken the decision to actively support the strike action lightly.
The action started on Thursday 20 February and is to culminate with a week-long walkout from Monday 9 to Friday 13 March.
The full strike dates are:Week one - Thursday 20 & Friday 21 FebruaryWeek two - Monday 24, Tuesday 25 & Wednesday 26 FebruaryWeek three - Monday 2, Tuesday 3, Wednesday 4 & Thursday 5 MarchWeek four - Monday 9, Tuesday 10, Wednesday 11, Thursday 12 & Friday 13 March.
Watch Paul Reilly's report: