A marathon election campaign has placed public servants in the delicate position of assisting the government with crucial budget and policy announcements, despite caretaker mode likely to begin in three weeks.

The election campaign will not be officially launched until after the May 3 budget when parliament is dissolved, which provides the government with a short period of time to push through key policies before entering caretaker mode.

Among the expected announcements is the successful bidder for Australia's $50 billion new submarine fleet with Japanese, German and French contractors waiting for confirmation.

It also provides an opportunity to use taxpayer money to fund advertising campaigns to spruik announcements. Melbourne-based Dentsu Mitchell has been awarded $7.9 million to sell reforms to food labelling laws, which comes into effect in July.

The multimillion dollar deal, signed on Monday, will see government messages carried across television, radio, print and social media during the campaign. The 12-week contract will expire just days before the election.

The deal comes amid reports the government has used taxpayer money to film a television campaign to sell $16 billion in savings over four years to be announced in the federal budget.

Prime Minister Malcolm Turnbull did not rule out using taxpayer funds to sell budget announcements on Tuesday, which prompted the opposition to complain of blurred boundaries between government business and campaigning.

Opposition leader Bill Shorten said the budget process was "fundamentally damaged" as it coincided with a 75-day election campaign.

Former Finance deputy secretary Stephen Bartos said taxpayer-funded advertising campaigns were "perfectly legal" until the caretaker period, but raised ethical questions given a July 2 vote had all but been announced.

Mr Bartos said many public servants could be pressured to finalise projects so they could be sold to the public during the campaign.

"It is quite likely the public service will be placed under pressure by ministers to accelerate some [of] the processes of government so they can be wrapped up before an election," he said.

"What they choose to push through will be determined by the contents of the budget and that has been mostly kept under wraps so far."

Centre for Policy Development chief executive Travers McLeod said there was no need to be concerned about the public sector's professionalism in difficult circumstances.

"One thing the public sector has clearly displayed in recent times is that it is effective, hard-working and dedicated enough to deliver on the often unreasonable demands governments have placed on it," he said.

"This will be no different."

The election campaign also raised challenges for Employment Minister Michaelia Cash, who is tasked with securing revised enterprise agreements for several key departments after  18 months of deadlock.

Union official David Smith, who represents Department of Defence employees, has called for a vote scheduled for 21,000 civilian staff to be delayed until after the election.

"Now the prime minister has confirmed the election date of 2 July, it really is inappropriate to proceed to further agreement votes when we, if not technically, are effectively in a caretaker mode of government," he said.

Under current rules, enterprise agreements can be finalised during the caretaker period and do not require a minister's signature as previously required.