Balpa fears a government "double whammy" with both the chancellor and transport secretary set to make statements on Tuesday (12 May).
Sunak is expected to set out his vision for the future of the country’s coronavirus furlough scheme, which expires at the end of June.
The scheme currently allows employers to stand down employees on 80% of their wages, up to a maximum of £2,500 a month, which the government will pick up.
Transport secretary Grant Shapps, meanwhile, is expected to offer further clarity on measures set to affect aviation, including details of the government’s proposed two-week quarantine for arrivals.
"Any reduction in the JRS scheme by the chancellor, or any restrictions placed on airlines trying to restart, would be terrible news for the industry, which has largely been grounded by coronavirus," said Balpa.
"Balpa has repeatedly called for the government to work with the industry but to no avail. The government seems to have its head stuck in the sand when it comes to UK aviation. It has failed to provide the support so urgently needed to help see this important driver of the economy through this crisis, and has refused to pull together a strategic plan for aviation.
"This is not about bailouts for failing companies; this is about supporting an industry that is suffering through no fault of its own."
Last week, Balpa wrote to the chancellor to seek financial support for the sector, while Airlines UK, the trade body for UK registered airlines, wrote to the prime minister about the quarantine measures he announced on Sunday night (10 May), which were trailed for several days in advanced of the announcement.
Balpa general secretary Brian Strutton said: "Tens of thousands of aviation workers have been furloughed and rely on the JRS scheme to pay their bills and feed their families. If JRS levels are reduced, it will be a bitter blow to those who have already seen their income reduced.
"Airlines are running out of cash and if restrictions are placed on their ability to return to flying then the government is plunging aviation further into a death spiral. Airlines, airports and workers are all saying the same – the government has got to start helping aviation, not destroying it."
