Can an ex-employer take any legal action against an employee for joining a competitor?

IF you have signed any kind of non-competition contract with your employer and have any secrets related to his business, he can stop you from working in a competitor company with a specific time and jurisdiction, however, an ex-employer can't bar you from being employed by any other company and different territory.

UAE Labor law Under Article 127 states:

“If work assigned to the employee allows to acquaint with the employer's clients or have access to the secrets of his work, the employer may oblige the employee that after the termination of the contract, he may not compete with him or take part in any business interest competitive to the employers. Such agreement shall be valid only if the agreement is limited with respect to the place, time, and nature of work to the extent as is necessary to safeguard the lawful interest of business”.

Therefore, if you are working in another geography, then I don't think you will be liable for breach of contract.

For more information, I need to check your contract.

You may contact me directly via phone or email for further consultation.