Kevin Pietersen thinks Test cricket should be worried by Tymal Mills' IPL contract
England international Mills, 24, only plays T20s, having retired from 50-over and four-day cricket due to a congenital back condition.
Pietersen is also a T20 specialist these days at the age of 36 and has played for franchises in India, Australia, South Africa, Pakistan and West Indies.
And he believes that Mills' big-money move to Royal Challengers Bangalore should be a wake-up call to Test cricket.
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"Another SLAP in Test cricket's face yesterday," Pietersen said on Twitter.
"A T20 specialist becomes one of the current England team's richest players.
"I don't blame him at all.
"I love how T20 is growing the game.
Tymal Mills is expected to be a key player in the IPL
"I'm just saying that Tests are falling way behind at the moment.
"ICC needs to act and quick."
Pietersen himself has not played Test cricket since 2014 having been sacked over dressing-room tensions in the England side.
But the South African-born batsman has been in hot water before due to his T20 ambitions.
Tymal Mills is a T20 specialist and gun-for-hire
In 2012, he was dropped for the Lord's Test in a dispute with his employers which reportedly emanated in part from his desire to play in the lucrative IPL.
However, the 36-year-old is not dismissing the longer form of the game, even if he did sacrifice his Test career for the 20-over format.
"I embraced [T20] eight years ago and it's what caused me my P45," Pietersen added.
"I absolutely love how all these youngsters are now benefiting!"
Mills is one of eight Englishmen who will play in the IPL this year, with Ben Stokes, Chris Woakes, Eoin Morgan, Jason Roy and Chris Jordan all being bought in the auction and Jos Buttler and Sam Billings being retained by their 2016 teams.
New Test vice-captain Stokes fetched the largest amount ever paid for an overseas player when the Rising Pune Supergiants forked out £1.7million for his services.
"It's a life-changing amount of money," said Stokes.
"I'm struggling to put it into words.
"I hadn't thought about how much I would go for.
"I guess having more than one team wanting me was probably the best position to be in."