Britain's Prime Minister Theresa May waits to greet Abu Dhabi Crown Prince Sheikh Mohammed bin Zayed al-Nahayan at Number 10 Downing Street in London, Britain, February 23, 2017. REUTERS/Stefan Wermuth

LONDON (Reuters) - Prime Minister Theresa May wants to see legislation giving her the right to trigger talks for Britain to leave the European Union approved by parliament’s upper house without any changes, her spokesman said on Wednesday.

May’s Brexit plan is facing its first major setback, with the House of Lords set to vote later on Wednesday in favor of forcing her to guarantee the future rights of EU nationals living in Britain.

“We would hope to see the bill progress unamended,” May’s spokesman told reporters.

The government has said it wants to guarantee conditions for EU nationals, but says it will only do so when all other member states agree to a reciprocal arrangement for Britons living abroad.

“The prime minister has been clear on many occasions that it is an important area for us and it is one that she would hope to see dealt with as a priority once the negotiations get underway,” he said.