Instructions: In this task, you are given an article. Your task is to summarize the article in a sentence.
Input: The proposed link would include a 3.1 mile (5km) tunnel between the Great Western main line at Slough in Berkshire and the airport's Terminal 5.
But Network Rail said a planning application, due to be submitted in the next few weeks, had been delayed until late 2017.
Businesses said the link was needed to attract more people to Reading.
Nick Halstead, who owns technology business Datasift in Green Park, said the "disappointing" delay was making it harder to attract staff.
He said: "The delay is not a good sign for this project and other projects where Reading should be seen as important."
Slough Labour MP Fiona Mactaggart said the delay showed "a failure of leadership" by the government and was "pathetic".
Tim Brownstone, who runs Reading sportswear company Kymira, said the rail link was needed to bring external investment to the area.
In November, a review of Network Rail's investment programme by Sir Peter Hendy concluded a number of projects including this one would take longer than planned.
Julian Burnell, from Network Rail, said the delay was "not really anybody's fault"  and changes had to be made following the Hendy Report.
He said: "It's a brand new tunnel, it's an entirely new stretch of railway, and that takes a lot of time and a lot of careful planning."
A Network Rail spokeswoman added consultations with landowners and interested parties in the area also had to be completed.
Given the go-ahead by the government in 2012, it was originally planned the new service would be in operation by 2021.
The plan would save up to 30 minutes for passengers travelling from south Wales, the west of England and the Thames Valley.
Output:
A delay of almost two years in building a new £500m Heathrow rail link has been criticised by businesses.