South Down MP Margaret Ritchie says Warrenpoint Harbour must not suffer because of Brexit.
She was speaking after a presentation by the harbour's CEO Peter Conway to the Select Committee in Westminster.
Mr Conway told the committee the port's imports and exports to Ireland amount to nearly 50% with a turnover of £5.5 million.
And he warned Brexit could force it to compete on an uneven playing field.
Mrs Ritchie says with the port just 50 metres from the EU border it's important nothing changes.
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