NI firm Almac says its decision to buy a factory in the Republic of Ireland was as a direct result of Brexit.
A major part of the Craigavon-based business is making products for big drugs firms.
It told a Commons committee its customers need it to have a presence in the EU for regulatory reasons.
It said it could face dual processes such as having to certify a product both in NI and Ireland so it can be sold in the EU.
Almac has also warned it may have to move some work to the Republic of Ireland from Northern Ireland, depending on post-Brexit arrangements.
Company director Colin Hayburn described the Irish facility, in Dundalk, as "a safety net".
He said it would have "minimal" operational requirements in the short term, but could be ramped up when needed.
Mr Hayburn added that if EU-UK regulatory equivalence was achieved as part of Brexit, Almac "should be fine".
But if that equivalence is not achieved it would be a "difficult situation", he added.