Tory leadership hopefuls are battling to secure the support of their colleagues, ahead of the first MPs' vote in the contest for No 10 later.
The eight candidates who have made it onto the ballot paper will have to secure at least 30 votes to stay in the race to become prime minister.
It is the first of a series of secret ballots over the next few days to whittle the field down to a final two.
It comes as Penny Mordaunt launches her leadership campaign.
She joins Kemi Badenoch, Suella Braverman, Jeremy Hunt, Rishi Sunak, Liz Truss, Tom Tugendhat and Nadhim Zahawi on the ballot, as all have secured the required 20 nominations from Tory MPs to make it into the first round.
As the race to secure votes steps up a gear, Trade Minister Ms Mordaunt pledged to slash VAT on fuel and raise income tax thresholds.
Setting out her stall at a hot, crowded launch event, she also promised parents more flexibility over subsidised childcare and said she would give MPs control over "social capital pots" to spend on their local areas.
Pitching herself as a team player, she said if she won office she would introduce a "tighter" cabinet of ministers with powers across Whitehall.
Adding that the Conservative Party had "lost its sense of self", she also vowed to return to the values of "small state, low tax, personal responsibility".
Ex-Health Secretary Sajid Javid and junior minister Rehman Chishti have dropped out of the race, after failing to pick up enough support.
The 30 vote threshold - which has been introduced to quickly narrow the field - could see a number of further candidates knocked out.
Wednesday's ballot will see voting start at 13:30, with a result expected at 17:00 BST.
Candidates will also appear at two further hustings events, as the race to secure endorsements heats up.
It comes as:
The campaign so far has laid bare Tory divisions over taxation, with a number of candidates attacking the rise in taxes under Mr Sunak's chancellorship.
All the contenders are pledging to bring in immediate tax cuts if they win, apart from Mr Sunak who says cuts should wait until inflation goes down.
Among those promising to reduce taxes, there are divisions over which taxes should be cut, and how quickly.
In an interview with the Daily Telegraph, Mr Sunak said tackling inflation is his "number one economic priority", and claimed former Prime Minister Margaret Thatcher, an icon on the right of the party, would have backed his approach.
But on of Ms Truss's backers, Mr Rees-Mogg attacked his record at the Treasury, telling Sky News the "tax-increasing chancellor" had made decisions "of the left rather than on the right".
And he sought to disparage Leave-voting Mr Sunak's Brexit credentials, branding him an "ostensible Brexiteer" whose department had resisted ending the "supremacy of EU law" during his tenure.