Another Commons showdown over Brexit is looming after the Lords inflicted a double defeat on the government.
New problems for prime minister Theresa May were signalled when an alliance of opposition peers, crossbenchers and Tory rebels backed seeking to retain the option of a customs union with the EU.
In a second setback for the government over the EU (Withdrawal) Bill, peers supported measures ensuring that existing protections across a range of areas including employment, equality, health and safety and consumer standards cannot be changed except by primary legislation.
Shadow Brexit Secretary, Sir Keir Starmer, said: "Labour has long championed the benefits of a customs union as the only viable way to protect jobs, support manufacturing and help avoid a hard border in Northern Ireland after we leave the EU.
"Theresa May must now listen to the growing chorus of voices who are urging her to drop her red line on a customs union and rethink her approach."
A Department for Exiting the European Union spokeswoman said: "The amendment does not commit the UK to remaining in a customs union with the EU. It requires us to make a statement in Parliament explaining the steps we've taken.
"Our policy on this subject is very clear. We are leaving the customs union and will establish a new and ambitious customs arrangement with the EU while forging new trade relationships with our partners around the world."
Pro-Europe Tories have pledged to make membership of a customs union a key issue when the flagship Brexit legislation returns to the Commons next month.