June 24 (Reuters) - Budget airline Spirit Airlines on

Tuesday urged the Transportation Department to reject a proposed

JetBlue Airways ( JBLU ) and United Airlines

partnership, saying it was anticompetitive and will prompt large

carriers to pursue similar deals.

United and JetBlue ( JBLU ) said in May the "Blue Sky" tie-up would

allow travelers to book flights on both carriers' websites,

while interchangeably earning and using points in their frequent

flyer programs. Spirit said the deal would mean the smaller

JetBlue ( JBLU ) "will become a de facto vassal of United." Spirit added

"this anti-competitive tie-up involving a dominant legacy

carrier will neutralize the competitive benefit of an existing

low-fare competitor."