The purpose of this paper is to answer the question whether investors may challenge domestic labour legislation by invoking breach of international investment agreements, in particular violations of fair and equitable treatment standard, as well as illegal expropriation of investments. The answer to this question is especially relevant for developing countries, such as the Republic of Serbia, which seek to harmonize their legal systems with international principles of labour rights protection. Therefore, the paper will explore the interpretations of the fair and equitable treatment standard and indirect expropriation given by arbitration tribunals and accepted among scholars, as well as their application with respect to the labour regulation changes. Particularly analysed is the relevant case law before arbitration tribunals dealing with the question whether host states may violate these standards by amending their domestic labour legislation. Research has shown that domestic labour regulation amendments may rarely be interpreted as indirect expropriation, while the fair and equitable treatment standard may be breached in case of unpredictable labour legislation changes which would significantly violate guarantees given by the state to attract foreign investments but cannot protect investors from the introduction of bona fide labour regulations.