University staff are walking out on the first of three days of strikes over pay, working conditions and pensions.
Lectures could be called off at 150 affected universities.
The National Union of Students is supporting the strikes, but some students are concerned about missing classes.
The Universities and Colleges Employers Association (UCEA) said the impact of the strikes on students had been "low and isolated".
Universities say they are putting measures in place to mitigate the impact on students' learning.