The local authority turned down a request for retention permission earlier this year.
The national planning regulator is investigating plans for a discount retail store in Westmeath.
The company behind Mr. Price - Corajio - is appealing Westmeath County Council's decision on its Athlone store to An Bord Pleanála.
It had applied for retention permission for its warehouse in Cornamaddy, but was rejected in April.
The company was not authorised to use the site - according to local authority planners - and granting retention "would set an undesirable precedent for similar developments" in future.
It also stated the out-of-town-centre location was not in line with efforts in the Westmeath County Development Plan to avoid urban sprawl.
The case is due to be decided by 26th September.
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