Is it permissible to be negligent at work, claiming the laws are unjust, after a fair job classification was changed, and is this considered a breach of the user’s obligations?

Contracts are binding on the contracting parties, and a lease is a binding contract for both parties. Neither party has the right to terminate it as long as the contract is valid.

However, after the contract period expires, either party has the right to refuse renewal or to add new conditions. If the other party agrees to these conditions, then it is binding; otherwise, they are not obliged to work.

If the worker agrees to the contract, he is not permitted to neglect his work or be absent from it, because he is entrusted with his work, and neglecting it is a betrayal of the trust, as Allah Almighty says: "O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know [the consequence]."