Wharfies at Sydney's Port Botany have been stripped of $120,000 worth of bonuses after stopping work at the busy docks due to poor air quality caused by bushfires.

Maritime Union of Australia branch secretary Paul McAleer said port operator DP World had cancelled a fortnight's worth of productivity-based bonuses for its 600 workers, who had "worked in good faith" to catch up on much of the time lost to "unavoidable" stoppages.

Workers at Port Botany have lost their Christmas bonuses. Credit:Peter Braig

The union is preparing to take the employer to the Fair Work Commission for docking 60 workers about $20,000 worth of pay over a six-hour work stoppage on December 5, when Sydney was blanketed in heavy, billowing smoke that was predicted to linger for two days.

"The fact the company did that is an act of bastardry, particularly going on Christmas," Mr McAleer told The Sydney Morning Herald.