A four-year collective agreement expired on Sept. 30.
The tentative deal will be presented for ratification on Sept. 12.
The manufacturer and Unifor have failed to reach an agreement on pension changes and benefit reductions.
The union says AltaSteel is making extreme demands and trying to undercut union representation.
Workers upset over replacement employees while two sides were in negotiations.
400 employees are back to work after two-day strike.
Workers at Quebec rail plant join Kansas aerospace makers on the picket line.
Despite record profits, Caterpillar wants to freeze wages and double health costs at Illinois plant.