Here are some of the basics of an employment contract/rules under Estonian law (the main legal act being Employment contract act).
An employment contract has to be in a written format. If the written format is not followed, it does not make the contract null and void. If a person starts doing work for which remuneration is considered normal, then an employment contract is deemed to have been concluded even if it is not in written. Needless to say, you should always demand a written contract. An employee can always demand information about his or her working conditions (for example a written contract) and the employer has an obligation to answer.
Also important, an employment contract cannot be amended unilaterally. So for example it is not possible to unilaterally prolong the agreed probation time for which the maximum term is 4 months. Also bear in mind that doing overtime or working on public holidays requires an agreement between the parties and cannot be forced upon an employee.
Finally, an employment contract can be terminated following very concrete conditions and procedures. Normally, it requires a significant breach of obligations to be „fired“ straight away – for example being drunk at work more than once. Legally, „firing“ someone is not easy under Estonian law and in cases where this is done illegally, an employee has the right to demand compensation for up to 3 months salary. Just keep in mind that the deadline for going to court or the Employment Dispute Board is 30 days from the receipt of the notice of termination.