I'm curious about whether your institution or department has an attendance policy for your lab-based classes?
For our courses that include a lab (i.e. - general chemistry with lab), our departmental policy is that if a student misses 3 labs, they fail the entire course.
For courses that are just lab (i.e. - inorganic lab, biochemistry lab), the policy can vary based on instructor. But if a student misses more than two labs, they probaly aren't going to do very well in the course anyways.
Just had to enforce the departmental policy this week for a student in gen chem, which got me thinking about what other schools do regarding absences in lab.