Landing Immigrants to Canada

I was informed by my company that "The U.S. State Department recently confirmed that Canadian permanent residents who are in the U.S. and who return to Canada will require a visa stamp in their passport before entering the U.S. This rule also applies to Canadian permanent residents who are returning under the 30-day rule if they did not previously obtain a visa stamp."

Do not know what does that mean. What if I have an expired visa? Has some one been to Canada recently? Please advise.

Thank you.