Gay marriages in Australia's Capital Terrority have been banned, just a few weeks after they were legalised.

The national Government argued that was inconsistent with federal laws.

Dozens of couples who've married since the law came into effect last weekend will now have their unions declared invalid.

It comes just a day after the justice minister announced that Ireland would recognise gay marriages legalised in six countries, including in Australia's Capital Territory.

Alan Shatter made an order recognising the unions in France, Brazil, New Zealand, Uruguay, Australia's Capital Territory and in six US States.

People in these relationships living in Ireland are now able to avail of the rights and entitlements that apply to Irish Civil Partnerships. 

Gay rights group GLEN said any couples based in Ireland who have availed of new laws in any of those countries will now enjoy equal treatment under tax laws.