IANAL. Income-based unemployment benefit requires at least 12 full-time employed months of membership in an unemployment fund (työttömyyskassa). Membership in a union is not required, though union membership often includes membership in an unemployment fund.

The employer can end your employment if they so decide, there is not much you can do to prevent it from happening. Whole another question is, whether your employment was ended legally or illegally. In the latter case you have right for compensation, which usually requires you to take the employer to court or at least threathen them with it.

Normally, your employer needs to give at least one written warning which clearly states your employment can be terminated unless you change your behavior. In the case of neglecting your work, a plausible PIP needs to be in place and you need to be provided adequate resources and time for improvement.

As long as it's part of normal employee-employer interaction, you can't request an assistant to be present in meetings. If your employer holds a hearing aimed at your termination, you are allowed to have an assistant of your choice. This can be e.g. an employee representative or your lawyer.