Nationalists are being unlawfully denied equal treatment by flying the Union flag at courthouses in Northern Ireland, a judge heard on Monday.
Lawyers claimed the practice of having the standard erected at full mast on designated days breaches a requirement to ensure parity of esteem for both communities.
Co Tyrone woman Helen McMahon is mounting a challenge in a bid to have the tradition quashed.
Ms McMahon, described as being a nationalist, centred her case on the Union flag being flown at Omagh courthouse.
But the judicial review was widened out to include all other court buildings where it is erected on set days throughout the year.
Her legal team contended that the requirement, contained in the Flags Regulations (Northern Ireland) 2000 goes against the Good Friday Agreement.
Martin O’Rourke QC told the High Court it defies a commitment to ensure equality for the identity, ethos and aspirations of each of the two main communities in Northern Ireland.
“It demonstrates the absence of any consideration of the parity of esteem provisions,” he argued.
According to counsel the solution could be to fly no flags on courthouses and public buildings.
“It’s not necessary to mark the constitutional position,” he added.
Tony McGleenan QC, for the secretary of state, disputed any suggestion of constitutional legal force to the parity of esteem concept, describing it as “unsound”.
He also questioned the timing of the challenge to regulations which came into force for court buildings eight years ago.
“The applicant gives no real information about herself or her interest in the process, other than to say she is a member of the nationalist community,” Mr McGleenan said.
“She does not explain how the flying of the flag at Omagh Courthouse impacts on her.”
Mrs Justice Keegan reserved judgment in the challenge.