More info:
A Congressional Research Service study notes that under the National Emergency Act, the president "may seize property, organize and control the means of production, seize commodities, assign military forces abroad, institute martial law, seize and control all transportation and communication, regulate the operation of private enterprise, restrict travel, and, in a variety of ways, control the lives of United States citizens."
The CRS study notes that the National Emergency Act sets up congress as a balance empowered to "modify, rescind, or render dormant such delegated emergency authority," if Congress believes the president has acted inappropriately.
NSPD-51/ HSPD-20 appears to supersede the National Emergency Act by creating the new position of National Continuity Coordinator without any specific act of Congress authorizing the position.
NSPD-51/ HSPD-20 also makes no reference whatsoever to Congress. The language of the May 9 directive appears to negate any a requirement that the president submit to Congress a determination that a national emergency exists, suggesting instead that the powers of the executive order can be implemented without any congressional approval or oversight.
Homeland Security spokesperson Russ Knocke affirmed that the Homeland Security Department will be implementing the requirements of NSPD-51/ HSPD-20 under Townsend's direction.
The White House had no comment.