U.K. Prime Minister Theresa May faces a battle with pro-European lawmakers in her Conservative Party after they grudgingly backed her plan to trigger Brexit negotiations by the end of March in its first test in Parliament.

The House of Commons Wednesday approved by 498 votes to 114 allowing May to start divorce talks with the European Union. But with more parliamentary hurdles ahead, lawmakers warned their backing shouldn't be mistaken for unconditional support to negotiate Brexit freely.

The government will publish a written outline of its Brexit plans on Thursday and it will lay out details of the clean break with the EU that the premier wants, including leaving the EU single market, overhauling membership in the customs union and controlling migration, with a period of transitional arrangements to help businesses adjust.