Immigration Site

How safe it to port the PD to another employer? I mean ,

1) When would the 140 revoke by the previous employer effect, is it before the 140 approval of the new labor / even after the new 140 approval.

lets say i ported the PD of Comapny As 140 to company Bs 140 while filing company B140. if the company A revokes before my company Bs 140approval, will that impact? also if company A revokes after COmpany Bs 140 approval, will that affect too. when would the revoke affects. At what stage i can use the company As 140 without affect, even if it got revoked . pls clarify, i am little confued on this topic...

Thanks a Lot