Technical problems halt the planned June 3 debut.
The carrier is slated to become the sixth participating airline by year's end.
The low-fare class doesn't allow refunds, changes or advanced seat assignments.
The expedited international arrival program soon will be in use at 24 airports.
Carrier will fly to Chicago, Dallas, Fort Lauderdale and Las Vegas.
The voluntary expedited screening program is now open at eight airports.
Europe's sixth largest carrier will add 70 destinations to the Oneworld network.
The Spanish airline served 19 domestic and 24 international destinations.
Houston's main airport will serve United's regional flights.
The arrangement expands the airlines' partnership.
Connectivity initially will be offered on flights to and from Los Angeles.
The carrier's top mileage members will qualify for the new screening in 2012.