Bringing orchid plants into a country (yours) presents some serious problems. There are two documents you must have, or the orchids will be confiscated and distroyed. One is an Export Permit from the country of origin, and the other is a Phytosanitary Permit. If the nursery the plant is bought from is big enough, they may be able to arrange for these, but it won't be cheap. The other item that would help, but may be overlocked for only a plant or two hand carried into a major airport, is an Import Permit, which can be obtained from APHIS for free if you live in the USA. It would help in cases like this if you would update your profile with your location.
http://www.aphis.usda.gov/permits/ppq_epermits.shtml
Plants in a flask should not require any of this, unless the agent at the airport is an ignoramous (it happens).