Speaker Tony Smith has announced that the five byelections will be held on July 28, sparking Labor fury because this puts Super Saturday on the last day of the ALP national conference.

Labor now faces having to postpone the July 26-28 conference, set to be held in Adelaide. Urgent discussions were underway in the party late on Thursday.

Smith, who sets byelection dates after consultation with the parties and the Australian Electoral Commission, told parliament the date – which means a nine-week campaign - had been advised by the AEC.

He said it allowed time for the AEC to implement the government’s new regulations to make candidates aware of their citizenship before nominating, and for candidates to comply with them. It also took into account school holidays.

The byelections, which span four states, are especially crucial for opposition leader Bill Shorten, because four are in ALP seats and two of those are on wafer thin margins.

The government would expect an advantage from publicity around whatever arguments there might be at the Labor conference.

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Labor’s deputy leader Tanya Plibersek said: “This is a disgraceful delay and a sneaky tactic from Malcolm Turnbull.

"It would appear this has been deliberately designed to disadvantage the Labor Party, given our national conference is scheduled for that weekend.

"This will obviously have implications for our national conference. Our activists will want to be out in the community campaigning for Labor, not sitting in a conference centre.”

The seats are Longman (Queensland), Braddon (Tasmania), Fremantle (WA), Perth (WA), and Mayo (SA). Mayo’s member has been Centre Alliance’s Rebekha Sharkie.

The contests in Longman, Braddon, Fremantle and Mayo have been caused by the citizenship crisis. All the previous incumbents are recontesting. Perth has become vacant because Labor’s Tim Hammond resigned for family reasons.

For the ALP the crucial contests are in Braddon which has a margin of 2.2%, and Longman which sits on 0.8%.

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The row saw angry exchanges in a Senate estimates committee between the Electoral Commissioner, Tom Rogers, and Labor’s Senate leader Penny Wong.

Rogers reacted sharply to Wong’s suggestion that the timeline looked “partisan”, compared to that in government seats in the past. “Are you saying I’m partisan?” he shot back.

He said the AEC put to the Speaker factors that needed to be considered - the selection of the date was up to the Speaker.

A 23 May letter from Rogers to Smith, which Smith tabled, said July 28 “is optimal”.

It “provides sufficient time for the AEC to implement the changes; enables prospective candidates to comply with the new requirements; and ensures that voters are not disenfranchised [due to school holidays].”

Rogers stressed in the letter that the AEC was only providing “advice” on the date. “The AEC remains ready to respond to any date you select”.

The next legally possible date was June 30, the letter noted. The AEC “is ready and would be able to conduct the byelections on that date”, Rogers wrote but then added the Speaker might care to weigh in his decision the issues of the changes to the nomination process and school holidays.

Rogers wrote that “rushing the process may risk providing an advantage to the major parties and disenfranchising independent and minor party candidates”, given the need to digest the changes and prepare nomination material.

Labor pointed out that other polls that had been held during school holidays.

Labor’s Justine Keay in Braddon will face former federal MP Brett Whiteley who held the seat from 2013 to 2016. In Longman Labor’s Susan Lamb faces former state MP Trevor Ruthenberg. Labor won Longman on One Nation preferences, which it won’t get this time.

The Liberals are not contesting the two WA byelections, although Liberal backbench senator Dean Smith will argue to the party’s state council on Saturday that it should run in Perth.

Michelle Grattan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.