A leading anti-Brexit Labour MP has said he and a "lot of people" are considering leaving the party.
Asked if he intended to quit, Pontypridd MP Owen Smith told the BBC: "I think that's a very good question, and I think it's something that I and a lot of other people are considering".
He and other Labour politicians have criticised Jeremy Corbyn for setting out terms for supporting a Brexit deal.
Mr Smith made a failed bid to topple Jeremy Corbyn as Labour leader in 2016.
Mr Corbyn made him shadow Northern Ireland secretary but sacked him from that role in March last year after Mr Smith called for Labour to back another EU referendum.
Asked by BBC Wales on Thursday if he would consider quitting the Labour party, Mr Smith said it was a question "I and people who hold my views will have to consider".
"The truth is that Brexit is not compatible with my values. It is a right-wing ideological project, it is a nativist project, it is fuelled by lies and it was delivered deceitfully in 2016.
"I got elected on a set of values which I think Brexit is incompatible with and I got elected to look after the people I grew up with and represent very proudly in Pontypridd.
"I don't think Brexit is reconcilable with those values and my desire to look after people in Ponty."
Mr Smith's comments came after Mr Corbyn wrote to the prime minister with five demands, including joining a customs union, that would need to be met for Labour to back the UK government on Brexit.
In the letter, Mr Corbyn offers talks to secure "a sensible agreement that can win the support of Parliament and bring the country together".
The terms include a "permanent and comprehensive UK-wide customs union" aligned with the EU's customs rules but with an agreement "that includes a UK say on future EU trade deals".
Commenting initially on Twitter, Mr Smith said Brexit, even on Mr Corbyn's terms, "would still shrink our economy, cost jobs and lost investment, indulge nativist nostalgia and isolationism... and pave the way for another austerity Tory government".
There was also criticism from other Welsh Labour politicians.
Gower MP Tonia Antoniazzi said: "Nice to be briefed about this @UKLabour @WelshLabour - if at ANY point you would like to consult MPs and also take the Labour Party conference motion into consideration... Just let me know... Cheers..."
Blaenau Gwent assembly member and former Welsh Government minister Alun Davies said Mr Corbyn "appears to be walking blindly towards a Tory Brexit and political oblivion. Whatever happened to our members determining policy and priorities?!"
But Aberavon MP Stephen Kinnock, who has been promoting what is known as the "Norway Plus" model of a close economic partnership with the EU, welcomed Mr Corbyn's letter, tweeting "This can break the deadlock."
"It also throws down the gauntlet to May because it has a seriously good chance of commanding a cross-party majority," he said.
Wrexham MP Ian Lucas called on fellow Labour MPs to back Mr Corbyn because "the government and parliament is paralysed because we haven't been able to reach a resolution".
"There is a consensus for a deal something like Jeremy Corbyn has set out in his letter," he said.
"I was elected on a manifesto commitment that we were going to be leaving the European Union.
"Those who supported Remain like me had to accept the referendum result in 2016."
There was also support for Mr Corbyn from the Welsh Government 's Brexit Minister Jeremy Miles, following a meeting of UK and devolved ministers at Westminster to discuss EU matters.
"This morning's letter from the leader of the opposition demonstrates that there is a deal that can gain wider support if the UK government will move on their red line positions," he said in statement.