Strathclyde Partnership for Transport (SPT) announced last month that Subway users who buy paper tickets would see the cost of their travel increase.
But customers who choose to use the new Smartcard scheme were spared the fare hike.
Subway passenger, Erin Leggate, who uses the underground twice a month, was "shocked" by the increase.
The 25-year-old, said: "I don't use the subway that often, so to find a return was £3 was a bit of a shocker.
"I would now consider getting on a bus. Rather than get a smartcard, I would be better paying a pound for the bus."
Single journey prices will remain the same on smartcards, at £1.40 for an adult and 70p for a child. An adult single increased by 20p to £1.60, a return by 40p to £3 and an all-day ticket by 20p to £4.
Return tickets, which did cost £2.60, are not available for people using the new plastic card. Instead they can buy a new daily ticket, for £2.70, which allows them to travel as often as they like.
It replaces the former all-day ticket which cost £3.80.
Strathclyde University student, Ali Mughal, 17, said: "It is pretty bad.
"Last month I was paying £2.60 and now I am paying £4 each day."
However, other passengers were more understanding about the price hike.
Liz Boyd, 56, said: "I think the price rises in general are necessary to upgrade the system and keep things running efficiently."
SPT says Smartcard holders will be guaranteed the best prices available for Subway travel.
A spokeswoman said: "We would urge anyone who has not yet registered for their own Smartcard to go online.
"It only takes a minute, it's free and you can top it up at your own convenience and save money."