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This issue should be covered by your contracting company's contract with its client.
In general however, the client is not likely going to want its proprietary information (client data, work files, etc.) shared with its contracting company. If you are in doubt, you should ask the client for instruction (if this becomes a dispute over intellectual property and/or intentional interference with economic advantage, the client is the one that has the rights over this information). But you should have gotten much more instruction regarding this issue from the contracting company when you were assigned.