Barrow failed to score for the fifth game in a row as Braintree moved above them in the Blue Square Bet Premier.
Aswad Thomas fired the visitors into the lead from 18 yards after latching onto Sean Marks' header.
Jai Reason struck from the spot after Marks was fouled by Gavin Skelton, before Ben Wright turned in Reason's cross to make it 3-0 at the break.
Substitute Jamie Guy struck from close range late on, the 15th goal Barrow have conceded in their last five games.
VIEWS FROM THE TRAINING GROUND
Barrow manager Dave Bayliss told BBC Radio Cumbria:
"I'm massively shocked and we expected a reaction (after their 7-0 defeat against Mansfield) and that's the reaction they have given us which is nowhere near good enough.
"It's the manner in which you get beat and the first half was disastrous.
"I honestly don't know if the lads thought 'well the season's over and I've done enough to earn a new contract', but those players are fast walking away out of this football club."