It looks like Bill Ackman is trying Jekyll-and-Hyde tactics to shake up Automatic Data Processing’s board.

The activist investor’s hedge fund Pershing Square said Wednesday that it wants to replace three of ADP’s board members as he pressed the payroll processor to cut costs and update its technology.

That’s an abrupt turn from last week, when Ackman told ADP’s board in a letter that he preferred to avoid a proxy fight and instead have his three nominees added to an expanded board.

“The directors we seek to replace do not have technology or industry expertise, a criticism ADP has leveled at our nominees,” Pershing Square said in a statement Wednesday.

The three, non-tech-savvy ADP directors in question include “a business school dean, and two former industrial sector CEOs,” Pershing Square added.

Ackman’s conciliatory tone toward ADP turned sour Tuesday after the New Jersey-based firm released a presentation that dismissed the qualifications of Ackman and his two nominees — and pointed out Pershing Square’s botched investments in Valeant Pharmaceuticals, JCPenney and Target.

Ackman’s $9.7 billion hedge fund initiated an 8.3 percent stake in ADP last month and holds only 2 percent of the company’s voting shares. ADP’s annual meeting will be held Nov. 7.

Reps from ADP declined to comment.