Wharfies at Asciano's Port Botany container terminal, Patrick's, have been put on notice that they could be locked out if they proceed with a planned strike on Wednesday.

The Sydney container terminal employs around 220 people, and wharfies plan to strike for 48-hours starting at 6am on Wednesday due to a rostering dispute in negotiations over a national new enterprise bargaining agreement.

Wharfies are planning to strike at Patrick's Port Botany container terminal on Wednesday. Credit:Peter Rae

Paul McAleer, the Maritime Union of Australia's Sydney branch secretary, said the union had "lost patience" with Asciano, despite being "very close" to striking a new wage agreement after a year of talks.

The union and Asciano had been unable to reach agreement on a new rostering system that would involve wharfies working more midnight and weekend shifts, Mr McAleer said.