The Unite union are meeting to decide who to back as the next leader and deputy leader of the Labour Party.
Candidates need support from two unions and an affiliate group to make it onto the final ballot if they cannot secure backing from 5% of local parties.
A complaint has been made against former Commons Speaker John Bercow by a previous senior adviser.
Lord Lisvane, who served as Clerk of the House between 2011 and 2014, said he submitted the formal complaint to the Parliamentary Commissioner for Standards on Wednesday.
Boris Johnson has dismissed calls to reform tax and benefit rules after claims some Greggs staff can only keep a quarter of their annual bonus.
The bakery chain has awarded 25,000 staff members a £300 bonus after a "phenomenal" year.
Jess Phillips is set to pull out of the race to be the next Labour leader.
The Birmingham Yardley MP is expected to release a statement later amid speculation she will announce she is withdrawing from the contest.
The UK's post-Brexit immigration system will put "people before passports", Boris Johnson has said.
Speaking at the UK-Africa Investment Summit, the PM said immigration would become "fairer... treating people the same wherever they come from".
EU citizens will not automatically be deported if they fail to sign up to the settled status scheme by the 2021 deadline, Downing Street has said.
The confirmation comes after European Parliament Brexit co-ordinator Guy Verhofstadt said