Praise be to Allaah.
Striking is a breach of the contract between the worker and his employer, and Allaah calls on us in His Book to honour and uphold the contracts that one person may take upon himself towards another person. So the worker has to do all the work that he agreed to do in a manner that pleases Allaah and in accordance with the aayah (interpretation of the meaning);
“O you who believe! Fulfil (your) obligations…” [al-Maa’idah 5:1]
Strikes are often accompanied by trouble, discord and violence, which is unacceptable in Islam because of the Fiqhi principle that warding off evil takes priority over achieving benefits. There are a number of other means which can be resorted to in order to achieve one’s goals, and which may be more effective than striking. A wise man would not leave any legitimate avenue unexplored.
As for stopping work because one has not been paid, this is permissible, because in this case the employer is in breach of contract, so the worker has the right to stop work until he gets paid. The Prophet (peace and blessings of Allaah be upon him) said: “Give the hired worker his wages before his sweat dries.” (Narrated by Ibn Maajah). And Allaah knows best.