Prime Minister Jacinda Ardern will announce a "minor" Cabinet reshuffle at her post-Cabinet press conference at 3pm today.

The reshuffle comes after weeks of intense pressure on Police Minister Poto Williams.

Last week, National leader Christopher Luxon called on Ardern to sack Williams and in question time, Ardern would not say whether Williams would stay on as police minister after the reshuffle.

Williams is likely to stay on in Cabinet, but lose the police portfolio. She also holds the less high-profile building and construction portfolio.

There's also mounting pressure on Nanaia Mahuta who holds the portfolios of local government and foreign affairs.

She's unlikely to be dumped from Cabinet completely, but may possibly be relieved of one of her portfolios to focus on the other.

The question is which portfolio she might be relieved of. As Local Government minister, she is the author of the Government's controversial Three Waters reforms.

The main piece of Three Waters legislation passed its first reading last week (at least two more bills are coming), which could give Ardern an excuse to relieve Mahuta of that portfolio so she could focus on foreign affairs.

However there are questions over Mahuta's performance in that role too - particularly her apparent aversion to the intense travel schedule the job requires.

Ardern might also decide it's time to shift MPs who are expected to retire from Parliament at the next election like Broadcasting Minister Kris Faafoi.

Faafoi is overseeing the establishment of a new public media entity. The entity has an establishment board and secured a big funding boost in the Budget. Faafoi would naturally want to stick around until the new entity is switched on next year, but Ardern might want to get a new minister into the role, giving them time to get their feet under the desk before defending the government's record at next year's election.

Labour's caucus met this morning. Ardern retains the privilege of distributing portfolios, but elevating MPs to the executive requires the vote of caucus.

Whip Kieran McAnulty has long been tipped for a promotion, and could replace Williams as police minister. However, Ardern might not want to baptise McAnulty's elevation to Cabinet with such a contentious portfolio.

Depending on what Ardern means by "minor" we could see the promotion of some members of the class of 2020 to roles. These jobs probably won't be elevated to full Cabinet positions.

Should deserving ministers outside Cabinet like Priyanca Radhakrishnan be elevated to a full Cabinet position, or Parliamentary under secretaries like Deborah Russell receive a ministerial promotion, it would create opportunities for high performers from the classes of 2017 and 2020 to get their foot in the door of the executive.

Keep an eye out for Barbara Edmonds, who could be given a revenue or financial role, or Rachel Brooking, who could be given a job helping Environment Minister David Parker with the Government's sweeping RMA reforms.