One fifth of enrolled Tasmanian voters will go to the polls in Montgomery, Nelson and Pembroke on May 4.

There has been speculation that Prime Minister Scott Morrison will call the federal election for May 11.

The Tasmanian Electoral Commission will issue the writs for the Legislative Council elections on Monday and voters will have until 6pm on Monday to ensure they are enrolled to vote.

Under the Commonwealth Electoral Act, no state elections can be held on the same day as the federal election without the permission of the Governor General.

Tasmanian Electoral Commissioner Andrew Hawkey said the May 4 election date would not be postponed.

"The writs will be issued and people will have to enrol to vote by 6pm Monday," Mr Hawkey said.

Political analyst Kevin Bonham expects there will be confusion among voters.

"It will be an issue because people will see signs up and get pamphlets for both elections," Dr Bonham said.

'If it is a week, or even two weeks later you won't be able to avoid the problem.

"Many people will not realise they will have to vote twice."

Dr Bonham said in 1996 the state and federal election had been held a week apart.

"It has come up before because in 1996 but not recently," he said.

There are 27,966 voters already enrolled to vote in Montgomery, 24,037 in Nelson and 22,876 in Pembroke.

Nominations from candidates will close on April 11 with all candidates to be announced on April 12.

In Montgomery, LIberal Leonie Hiscutt is seeking re-election.

For the first time in recent history, Labor will contest Montgomery with teacher Michelle Rippon standing.

Sitting Labor member Joanna Siejka is seeking to be elected for six years in Pembroke.

In Nelson a huge field is vying for retiring member and Legislative Council president Jim Wilkinson who has held the seat for 24 years.

There have been changes to electoral boundaries which came into effect in 2017.

The new division of Montgomery now includes the Central Coast municipal area, and the Burnie City municipal area generally east of Shorewell Creek and south of Hillcrest and South Burnie, including Acton, Brooklyn, Romaine, Emu Heights and Havenview, and the Western side of the Kentish municipal area including Sheffield and Paradise.