With just days left before the UK’s official Dec. 31 split from the European Union, the British government is urging businesses to prepare themselves for new changes.

Despite Thursday’s trade deal, which still allows zero-tariff and zero-quota access to the bloc’s single market, big changes are ahead.

“The deal is done, but with big change comes challenge and opportunity,” said British cabinet office minister Michael Gove.

“There are practical and procedural changes that businesses and citizens need to get ready for, and time to make these final preparations is very short.”

Originally, rules were to remain unchanged for 21 months after a Brexit deal, but when Brexit was delayed from March 29, 2019 to Jan. 31, 2020, the period was not extended.

Companies now have just days to understand and implement the 1,000 new pages of trade agreement rules between the UK and the EU and Northern Ireland. Notably, British businesses must now make customs declarations on goods to the EU and permits will be required to go to ports in Kent, or risk a fine.

According to the New York Times, many questions still surround the state of migrants and services, particularly within the financial industry, both of which were largely excluded from the trade deal.