Theresa May's minority Government and Labour both face significant tests in crunch House of Commons votes on Queen's Speech amendments on abortion rights for women from Northern Ireland and Brexit.
Ministers face a headache over an amendment tabled by Labour MP Stella Creasy, calling on the Government to provide funding so women from Northern Ireland can have abortions in England without having to pay.
It has the formal backing of one Tory MP, Sir Peter Bottomley, while others have expressed concerns over the issue, as abortion is illegal in Northern Ireland except where the life or mental health of the mother is in danger.
The Democratic Unionist Party (DUP), which is propping up the minority Government after securing a £1 billion funding boost for Northern Ireland, will oppose Ms Creasy's amendment.
But if it passes, it could raise questions over the viability of the Tories' "confidence and supply" agreement with the DUP, which would then have to vote for a Queen's Speech amended on Ms Creasy's terms.
A DUP source said the party would deal with the issue "one step at a time".
It is unclear if the Tories will follow Labour in allowing MPs a free vote as a "matter of conscience", but Speaker John Bercow's selection of the amendment surprised observers and has caused trouble for the Government.
Commons Leader Andrea Leadsom has attempted to quell Tory concern over the issue, telling MPs that the health and equality departments are "discussing and looking very closely at this issue today".
And Mrs May's official spokesman told a Westminster briefing: "The Government will respond later today".
Mr Bercow has also created potential trouble for Jeremy Corbyn by selecting an amendment which looks set to highlight splits among Labour MPs over Brexit.
A total of 43 Labour MPs have formally backed an amendment tabled by former shadow cabinet minister Chuka Umunna, which supports membership of the single market and customs union after Brexit.
The Labour leader will not support it as the party is committed to ending free movement of EU citizens and leaving the single market, but aims to retain the "exact same benefits" of the trade bloc.
It is unclear if Mr Corbyn will whip his MPs against supporting Mr Umunna's amendment, but any vote is likely to highlight Labour divisions over how to deliver Brexit.
Meanwhile, Labour has claimed Mrs May's programme for government is in "tatters" following her drubbing at the general election.
It has tabled a wide-ranging amendment which reproduces many of its manifesto policies and Mr Corbyn urged MPs of all sides to support it, claiming Mrs May has no mandate for continued austerity.
In an illustration of the wafer-thin majority the Government now relies on, the Prime Minister will head straight back from a meeting with other world leaders in Berlin to Parliament so she can walk through the voting lobby.
A Labour source said the party's official position is to abstain on Mr Umunna's amendment.
When Ms Creasy raised the issue of charging for abortion during the Queen's Speech debate on Wednesday, DUP MP Ian Paisley told the Commons "this is not a matter for Belfast, it is a matter for NHS England".
Tory MP Sir Peter Bottomley, who has signed the abortion amendment, suggested a "practical solution" would be found, such as forming a charity to help women in Northern Ireland access services so they "won't have to throw themselves at the mercy" of English medical bosses.
He told BBC Radio 4's World At One: "If you come forward with a result before the amendment is called, I don't have to vote for the amendment and everyone can say 'That's practical'.
"I believe we will have an announcement that is certain, is fair and does the equality job."
Sir Peter there are "too many" abortions but the legal restrictions were not the right way to deal with the issue.
"The answer is to make sure more of us think in advance. If you've already got five children, don't conceive another one.
"If we don't know who our partner is, ask their name before you sleep with them rather than afterwards, and if you don't intend to have a child try not to have a conception."
Sir Peter said women should not be prevented from having an abortion because they do not have enough money.
"I think two-thirds across the House, the Conservative Party and others, say you shouldn't discriminate against the poor," he added.