Town chairman David Bosomworth is calling on as many supporters as possible to make the trip to Cambridge and cheer the club on to victory.
The biggest home crowd of the season saw Halifax edge a tight game 1-0 on Wednesday thanks to Lee Gregory’s 83rd minute penalty.
Now Bosomworth wants another big show of support from the Town faithful for their 320-mile round-trip on Sunday.
He said: “Off the back of what we’ve seen on Wednesday all I can hope is that every single fan that feels they can do gets down to Cambridge.
“I think we’ve got 1,400 seats with probably another 600 on the terrace and I just hope we fill every place.
“We have one chance now so we want to try and finish the job.
“But Cambridge are going to be really strong on their own patch.
“It’s another 90 minutes, we’ve got to play to our best, the lads have got to get re-energised to go again.
“But we can’t do any better than we’ve done - to take a 1-0 lead is excellent.”
Bosomworth admitted there was extra pressure on the clash and is excited at being within touching distance of a place at Wembley.
He said: “I’m absolutely delighted because there was a lot of pressure on.
“When you reach this stage everybody wants to be able to get through to the next level.
“I think every Halifax fan, the players and the management, will be craving to come out at Wembley.
“We mustn’t get ourselves because it’s only the proverbial half-time but I’d rather be going to the Abbey Stadium with a 1-0 lead than being a goal behind.
“It was really tight, they had a couple of good chances.
“I’m very pleased with the crowd too, it was a tremendous turnout.”