Every election a close battle: Minister

Cabinet minister Simon Birmingham has played down a new opinion poll's knife-edge prediction for the upcoming federal election.

The Fairfax-Ipsos poll, conducted over the weekend, has the coalition and Labor locked at 50-50, assuming an allocation of preferences similar to those at the last election.

Federal MPs and senators are heading back to Canberra on Monday for the week's special sitting to vote on key legislation to restore the Australian Building and Construction Commission and the registered organisations bill.

Senator Birmingham said it was not surprising the contest was narrowing.

"Every Australian election is a hard-fought affair and a close battle," he told Sky News.

Employment Minister Michaelia Cash expected the polls to tighten in an election year.

"But the only poll that counts is the poll obviously on election day," she told the Nine Network.

Her cabinet colleague George Brandis also says margins narrow entering the "home stretch".

"These polls are pretty much where we would have expected them to be at this stage in the cycle," he told ABC radio.