The Foreign Affairs Minister says the EU is unlikely to ratify any Brexit deal if the UK is still making threats.
Simon Coveney has also warned that not nearly enough progress has been made so far in the negotiations.
He has also criticised the legislation being brought forward by Boris Johnson that would undermine parts of the already agreed Withdrawal Agreement - in particular the Northern Ireland Protocol.
Minister Coveney said the move to overwrite parts of the international agreement is deeply concerning.
He said: "If there is still a threat to legislate to undermine the Withdrawal Agreement and break international law... I don't believe any future relationship agreement will we be ratified.
"Why would the EU ratify a new agreement with a country that is threatening to break an agreement that's not even 12 months old?"
The British government's controversial legislation is currently moving through parliament, having passed its first key hurdle earlier this month.
However, it has prompted major criticism from both the EU and Ireland.
Prominent US politicians such as Nancy Pelosi and Democratic presidential candidate Joe Biden have warned there will be no US-UK trade deal if the British government undermines the Good Friday Agreement.