This is of course the most common human rights question that comes up, and one that can often serve as a ‘hot potato’ issue. The short answer is yes, but CAREFULLY.
The law states that an employee cannot be discriminated against in their employment because of those protected grounds noted above, which include disability, marital status, and family status. Terminating someone’s employment directly in relation to these would almost unquestionably be seen as discriminatory, and the financial penalties before a court or tribunal could be steep.
However, the law also recognizes that employers are required to make business decisions. In those cases these sorts of terminations are defensible provided that an employer can show that it was done for business reasons and not because of the protected ground. For example if an entire department is shutting down but one of the employees happens to be on parental leave, that may be sanctioned as a valid business reason so long as they are not the only employee let go while the others are moved to new positions.
Otherwise, the law requires that employees who may be unable to work due to a protected ground to be accommodated. For example if an employee breaks a bone and is unable to perform part of their duties, modifying their role or accommodating them in a new role for a short time will be seen as less discriminatory than an outright termination. Similarly, the law is clear that an employee who is on pregnancy or parental leave should be able to return to their role following their leave, and during that leave should have the same opportunities as if they had remained in the workplace (salary increases, promotions, etc.).
The bottom line is that you cannot dismiss them because they are on leave, but you can dismiss them while they are on leave for legitimate business reasons.