An employee can breach the terms of their employment contract by, among other actions or omissions, failing to carry out their duties, breaching restrictive covenants or by failing to give the correct notice of resignation.
In any event, where there has been a breach, the employer can sue the employee for any financial loss arising out of the breach. However, in most cases, particularly where the breach is minor, the employer may wish to resolve the matter internally. This might take the form of disciplinary proceedings or, where the employment contract allows for it, dismissal without notice. The two parties can also reach a settlement agreement to confirm the employee's exit terms.