Launching the Welsh Conservatives' election manifesto in Wales on Monday, the prime minister will tell voters they must chose whether she or Jeremy Corbyn negotiates the UK's EU exit.
The EU wants to begin talks 11 days after polling day, she will say.
It will be seen as a bid to move on the election debate after criticism of Tory social care plans in England.
No details have yet been released of the party's Welsh manifesto ahead of the 8 June vote.
The Conservatives are under pressure to commit to the Swansea Bay tidal lagoon project and confirm the main railway line in south Wales will be electrified as far west as Swansea - projects which will be promised for delivery by Welsh Labour during its own manifesto launch, also on Monday.
A promise to scrap the tolls on the Severn Bridges was made by the Tories last week.
During a visit to Wales, Mrs May will say: "The UK's seat at the negotiating table will be filled by me or Jeremy Corbyn. The deal we seek will be negotiated by me or Jeremy Corbyn.
"Every vote for me and my team in this election will be a vote to strengthen my hand in the negotiations to come. Every vote for any other party - Labour, the Liberal Democrats or Plaid Cymru - is a vote to send Jeremy Corbyn into the negotiating chamber on our behalf.
"That is the stark reality of the choice that we face - the choice we must focus on over the next 17 days."
She will say "ordinary working people" have too often been denied the support they need from the government.
"I know that sense of disenchantment is particularly acute here in Wales. We saw that when people across Wales chose to ignore the hysterical warnings of Labour, Plaid Cymru and Liberal Democrat politicians in Cardiff Bay, and voted to leave the EU," she will add.
"We see it now in the way those same politicians refuse to respect that vote as they try to find new ways to put obstacles in our way.
"And the cause of that emerging gulf is clear.
"It is because the Labour party has taken people in Wales for granted for decades - just as it has in other communities across Britain."
Theresa May is to insist there will be "no time to waste" in delivering a Brexit deal after the general election.