Icstis, the premium-rate phoneline regulator, said it will be looking into claims that Opera Interactive Technology only ever chose households with easy access for camera crews for the daily competition, which gives viewers the chance to win £20,000.
Freelance producer Steve Benham reportedly alerted Icstis to the potential problem, making an official complaint.
Benham said: "Every producer and director on location experiences logistical problems with getting camera crews to the 12th floor of a high rise block and I can sympathise with that.
"The fact is that there are thousands of people living in high rise blocks or hard to reach areas who are phoning in every week that will never stand a chance of winning."
Icstis has asked the producer to provide additional evidence to back up his claims, but it has also passed the complaint to media watchdog Ofcom.
A spokesman from the regulator said: "We will be asking both 'GMTV' and Opera to respond to this claim as part of our overall investigation."
This fresh complaint comes only days after the BBC's 'Panorama' claimed that a shortlist of winners to 'GMTV' phone-in quizzes had been chosen long before competition phonelines closed, costing the public around £10m a year, over a period of four years.
'GMTV' denied being involved in any wrongdoing and subsequently pulled its contract from Opera on Tuesday this week. On the same day Opera apologised "unreservedly" to 'GMTV' and competition entrants, and has promised to work with 'GMTV' and regulators to compensate those who lost out.
Other broadcasters have been caught up in the phone votes scandal, which has blighted the broadcasting industry. Ongoing action by the premium phoneline regulator Ictsis includes an investigation into phoneline activity during the 'You Say, We Pay' section of 'The Richard & Judy Show' on Channel 4, with an outcome due in May.
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