DUBLIN, June 10 (Reuters) - The United States' largest

online betting operator Fanduel will introduce a surcharge on

customer bets in Illinois from September, its owner Flutter

said on Tuesday, in its first such move anywhere in the

world.

The 50-cent transaction fee on each bet placed in Illinois

is in response to the state legislature's recent decision to add

a new tax on wagers from next month that will hit the sector's

dominant players Fanduel and DraftKings ( DKNG ) hardest.

FanDuel, which has a 43% share of the U.S. sports betting

market, will immediately remove the transaction fee if the state

were to reverse its decision at any point, Flutter said.

Flutter opted not to introduce a charge when Illinois hiked

its tax rate on betting firms last year, while DraftKings ( DKNG ) said

it would add a charge on customer winnings in high-tax states,

only to reverse the plans following customer feedback.

Flutter Chief Executive Peter Jackson said at the time that

the best response to higher taxes, based on its experience in

the more established European market, was to cut local marketing

or moderate customer offers, a strategy the company said offset

around 50% of the 2024 Illinois tax rise.

Flutter said on Tuesday that while "extensive efforts" were

made to absorb the cost of last year's tax hike without

impacting customers, it was disappointed that Illinois' new tax

will punish larger operators.

"It is important to recognise that there is an optimal level

for gaming tax rates that enables operators to provide the best

experience for customers, maximize market growth and maximize

revenue for states over time," Jackson said in a statement.

Analysts estimated last week that the new Illinois tax would

hit Flutter's core profit by around $74 million in a full year

without any mitigation measures.

Flutter expects to grow its group-wide profit by 35%

year-on-year to $3.18 billion this year, with just over a third

coming from the rapidly growing U.S. market.