An arbitrator commits a material error of law that renders an award unreasonable and reviewable when the arbitrator misconstrues the objectives of the LRA and a collective agreement, and fails to properly apply principles of interpretation of agreements. On interpretation of collective agreements: the court must apply the modern approach considering language, context, purpose and circumstances objectively; clear and unambiguous language must be respected; subjective considerations of fairness cannot override objective interpretation; different provisions contemplating different consequences for different types of conduct must be interpreted and applied separately and not artificially merged into one category; the context includes the objectives of the LRA (discouraging unprotected strikes) and the specific purposes and prohibitions in the agreement itself. Unprotected strike action, being prohibited by the LRA and violating its core objectives of orderly collective bargaining, is not part of the constitutional right to collective bargaining and may be treated more severely in collective agreements than other forms of misconduct. Where a collective agreement provides in clear language that employees who engage in rolling unprotected industrial action forfeit their project bonus, and no exceptions apply, employees forfeit the entire project bonus for the applicable period, not merely the bonus for the month in which the strike occurred.