Rugby fans who have paid up to £100 each on internet auction sites for tickets for Llanelli's sell-out European Cup game will be refused entry to Stradey Park.
Friday evening's game at Stradey Park is a 10,800 sell-out
The club is taking action to combat touts cashing-in on the Heineken Cup match against Biarritz on Friday.
Officials believe it is the first time tickets for a Scarlets game have ended up on the web way above face value.
They have traced the reference numbers after being alerted by fans desperate to be among the 10,800 in the ground.
The tough stance has the backing of the Scarlets supporters' club who say those selling tickets above face value are preying on genuine rugby fans.
The game was sold-out less than two days after tickets went on sale to the general public.
The club limited sales to two per person to try and stop them going on the black-market.
Despite this, the club said they have appeared on internet auction sites where they have fetched bids as much as £200 for a pair.
The highest priced tickets for the match were £25.
Llanelli's commercial manager Ross Evans said it was clearly stated on each ticket that they were not to be exchanged above face value as a condition of sale.
She said the club had worked with the European Rugby Cup (ERC) governing body to trace those that had ended up on auction sites.
"It's the first time we have been notified by different supporters that this has happened.
"We understand there are many people who want to see the game but do not have tickets.
"We've done everything we can to try and be fair with the allocation. Tickets were limited to two per person to try and stop any unscrupulous purchases."
She said the ERC had contacted internet auction sites and some had now stopped the sales.
People who had already bought black-market tickets would not be allowed into the ground.
"It is a sad situation for those who have paid for tickets this way," she added.
Supporters' club chairman Jason Richards said: "I know a couple of people with spare tickets and they have passed them on at face value to genuine fans - which is how it should be.
"I don't see the point in charging more - they are preying on people and just out to make a bit of money."