How to check Transaction from which WF has triggered from

Hi,

I have a requirement to check if a PO is changed from ME21n Tcode and if its of specific PO type, then it should go for approvals else it should directly release the PO without approvals.

I have created a Activity step type and got the PO Type from EKKO of current PO. However , I need to check the Tcode from which the PO was changed, How to get this information programmatically in workflow?

Appreciate your quick response.

Thanks,

Rahul.