Customers are being asked to tip even at self check-out. Some say it's 'emotional blackmail.'

• Tip cues are becoming more common at digital, self-checkout kiosks.
• But customers are unsure where the money is going or whether the prompt is necessary.
• The issue highlights a bigger phenomenon: "tipping fatigue."

Self-checkout machines at cafes, sports stadiums, and airports are asking people to tip — and customers aren't happy about giving their extra money to machines.

A recent report from The Wall Street Journal noted the rise of digital, self-checkout kiosks hitting customers with a tip prompt at the end of their transactions. This prompt has frustrated people who are being asked to tip workers with whom they've had no interaction.