The phrase "a major deadline" is correct and can be used in written English.
You can use it when talking about an important or crucial due date for a task or project. For example, "We need to finish this project before the end of the month. It's a major deadline and we can't afford to miss it."
Next month, truckers face a major deadline forcing them to adapt to a new technology and it's just the beginning.
But the personnel change comes as global trade negotiations are in serious trouble, with a major deadline just weeks away.
Your project team has a major deadline, but friends from college have invited you on a not-to-be-missed ski trip on the weekend just before it.
This year, the nuclear negotiations in the Swiss city of Lausanne, which are entering a critical phase ahead of a major deadline, are being debated over dried fruits, pistachio nuts and watermelon seeds.
In those rare cases where Democrats and Republicans have come together on a big issue in the last fifteen years, it has almost always been in the midst of genuine crisis, or when a major deadline (usually self-inflicted) looms.
International negotiations on Iran's nuclear programme have made dramatic strides towards a comprehensive agreement, according to diplomats at the marathon talks, now entering a critical last week before a major deadline.
Transportation officials said last week that they were pushing back by five months a major bid deadline for companies seeking to build and operate the $2.45 billion project.
Maryland transportation officials have pushed back by five months a major bid deadline for private companies seeking to build and operate a Purple Line, saying the firms requested more time to find cheaper ways to do the $2.45 billion light-rail project.
Administrators in particular are often swamped during the days leading up to a major application deadline.
In addition to speaking against the US health law, which conservative Republicans seek to defund before a major implementation deadline on 1 October, Sen Cruz also read the classic children's book Green Eggs and Ham by Dr Seuss as a bedtime story to his two children.
As Congress-watcher Sarah Binder pointed out on Twitter, often secrecy arises after long debates have led to an impasse, or when a major external deadline rushes Congress.
