"The wealth of evidence is indisputable and the need for mechanism of presumptive legislation is also indisputable," union secretary Wattie Watson said.
"We'd love to see an announcement."
ACC makes its decisions on a case-by-case basis, trying to determine whether cancer is more-likely-than-not work related.
"If a firefighter or former firefighter develops cancer and there is evidence that it was due to significant exposure to chemicals at work, then they may be covered," an ACC spokesman said.
But Watson said without umbrella legislation covering firefighters, there appeared to be no rhyme or reason to who received help.
"The current system isn't designed for those situations of where you can't name exactly what you've been exposed to," she said.
"A firefighter may go to thousands of these fires over their career."
The union is hoping the Government will follow the lead of Canada and Australia, which recognises a list of 14 specific cancers as being linked to firefighting and covers them automatically.
The National Party has promised to change the law as part of its election-year health policy pitch.
A spokesman for ACC Minister Iain Lees-Galloway said the issue was being considered seriously and he was expecting to receive advice from ACC in the next couple of months.
"It's not straightforward and involves considerable research and analysis. It's important to get it right," the spokesman said.
But Watson said it was not clear what more information could be needed.
"We have a huge amount of evidence," she said.
"This really shouldn't be a difficult thing."
An ACC spokesman said the organisation had been looking at the issue to see if coverage could be improved.
"Part of this work involves looking closely at overseas assessment criteria, as used in Canada and Australia, where factors such as cancer type, length of service and chemical exposure guide decision-making," he said.
"This is a complex and emerging issue and it's important we consider any new criteria carefully to ensure we apply the law fairly."
Those not covered by ACC can still receive treatment through the public health system.
But Watson said firefighters in the past had turned to donating leave to their colleagues or fundraising for each other in order to cover the loss of income.
"At the time they need it the most, they are not getting support," she said.