Everyone in the country has the right to be free of unreasonable police searches and seizures. This also applies to undocumented immigrants who stopped in public and at random by ICE agents. Most importantly of all, remember that you can stay silent, request a lawyer, and refuse any unnecessary search that is conducted before being placed under arrest; quick pat downs to search for weapons are not prohibited.
Your workplace is technically a private space. ICE agents cannot force their way inside if uninvited unless they have received a warrant first. Keep in mind that you should not attempt to flee the building. If you want to leave, then do so calmly, ask any intercepting ICE agents if you are free to leave, and never resist if you are not.
Many of your constitutional rights as an undocumented immigrant are the strongest when you are on your own property. If an ICE agent knocks on your door, you are not obligated to open it. You may want to at least respond to the person knocking at the door, though, as they might have a valid search warrant to enter the premises, with or without force. Remember that search warrants are printed out on single sheets of paper that can be held up to a window for inspection, or slid under the door.