US major Delta Air Lines looks set to retain its lucrative access at the capacity constrained Love Field Airport in Dallas, where limited gate space and previous legislation has significantly restricted previous airline growth to just local markets.

The airline currently offers five daily flights from the much coveted airport due to its proximity to central Dallas to its Atlanta hub at Hartsfield-Jackson International Airport, but has run into a bitter battle with the facility’s largest tenant, low-cost carrier Southwest Airlines, over gate access.

According to correspondence from the US Department of Transportation (DOT) this week, the City of Dallas, which owns the airport, has been told it must accommodate Delta at Dallas Love Field. “The City has the legal obligation to reasonably accommodate all air carriers seeking to provide service at Love Field,” said Kathryn Thomson general counsel for the US DOT in the letter to Peter Haskel, executive assistant city attorney at Dallas City Hall, dated June 18, 2015.

Southwest Airlines currently leases 18 of the airport’s 20 gates from the City of Dallas with the balance currently held by Virgin America. Delta is currently operating its service on a Southwest gate under a temporary agreement, which ends on July 6, 2015, but Delta believes that the city has the authority under Southwest’s lease to require it to make room for Delta over the long term.

However, the budget carrier is refusing to share the gate space moving forward longer-term. The lease deal at suited Southwest at the time it was agreed, but the removal of the Wright Amendment, a law passed in 1979 restricting the markets that could be served from Love Field to protect then-new Dallas/Fort Worth International Airport, means that accessibility has an increased value for Southwest.

“It is DOT’s view that making reasonable efforts to accommodate new entrants or other carriers seeking expansion at Love Field... follows the airport’s obligation to make the airport available on ‘reasonable conditions’ and ‘without unjust discrimination’,” said the correspondence.

“Likewise, efforts to accommodate new entrants or other carriers seeking expansion at Love Field ensure that the airport has not given an ‘exclusive right’ to a carrier at the airport,” it added.

As such, the DOT says that it believes that the City of Dallas “is required to accommodate a requesting carrier unless Love Field’s facilities are fully utilised at the time of the request, or the signatory carriers at the time of the request are selling tickets for future flights fully utilising the facilities”.

The City of Dallas says it has now been put in an “impossible situation” and has filed a lawsuit in District Court to seek guidance on the rights of other airlines that want to use Love Field’s increasingly in-demand gates.

“Mandates from two federal agencies under color of federal law and conflicting legal claims and litigation threats by several airlines under federal law have put the city in an impossible situation that only this court can resolve. An impending July 6, 2015, deadline that may cause chaos at Love Field requires the city to file this action now,” the lawsuit states.