I don't think Bill Mitchell's suggestion that declaration of a National Emergency can't be challenged by the 9th circuit or other "friendly" court is correct.
The National Emergencies Act does not provide a separate statutory authority, but rather it provides for the declaration of a National Emergency that then triggers authorities under emergency provisions in other legislation.
This means a court could challenge in two areas. First, the basis upon which the national emergency is declared. That must be set forth and explained. The second area is the actual emergency statutory authority that is triggered by the declaration. That could be in any of a number of places.
For example this is Obama's declaration of a National Emergency for H1N1. Note that he explains whey it's a problem, and appeals to actual authority under section 1135 of the Social Security Act. That is where to look for the actual authority.
So bottom line, it can be challenged, and thus it can be stopped pending appeals.
Obama's declaration:
"NOW, THEREFORE, I, BARACK OBAMA, President of the United States of America, by virtue of the authority vested in me by the Constitution and the laws of the United States, including sections 201 and 301 of the National Emergencies Act (50 U.S.C. 1601 et seq.) and consistent with section 1135 of the Social Security Act (SSA), as amended (42 U.S.C. 1320b-5), do hereby find and proclaim that, given that the rapid increase in illness across the Nation may overburden health care resources and that the temporary waiver of certain standard Federal requirements may be warranted in order to enable U.S. health care facilities to implement emergency operations plans, the 2009 H1N1 influenza pandemic in the United States constitutes a national emergency. Accordingly, I hereby declare that the Secretary may exercise the authority under section 1135 of the SSA to temporarily waive or modify certain requirements of the Medicare, Medicaid, and State Children's Health Insurance programs and of the Health Insurance Portability and Accountability Act Privacy Rule throughout the duration of the public health emergency declared in response to the 2009 H1N1 influenza pandemic. In exercising this authority, the Secretary shall provide certification and advance written notice to the Congress as required by section 1135(d) of the SSA (42 U.S.C. 1320b-5(d))."