** Shares of payments firm Fiserv FISV.O up 3.2% at $61.26 premarket

** Activist investor Jana Partners has built a stake in co, the Wall Street Journal reports on Tuesday, citing people familiar with the matter

** Size of Jana's stake and whether it plans to seek board seats remains unclear, per the report

** "We value shareholder perspectives as we drive progress through our One Fiserv action plan,” Fiserv says in a statement, adding it has engaged with Jana in recent months

** Fiserv has been reviewing operations since last year; CEO Mike Lyons has stressed improving forecasting discipline and reducing reliance on short‑term growth tactics

** As of last close, FISV stock down 11.6% YTD, following a 67.3% drop in 2025