A private equity firm has taken a 9.5% stake in BJ's Wholesale Club and said it may propose taking the warehouse club operator private, according to reports.

The firm, Leonard Green & Partners, thinks BJ's shares are undervalued and will talk with the company about taking it private, new financings and other options, Reuters wrote today (2 July).

The move sent BJ's shares up as much as 18% to a more than two year high, reaching US$43.83 a share.

Leonard Green & Partners also has investments in Whole Foods Markets, Rite Aid, Sports Authority, Davis's Bridal, Neiman Marcus and the Container Store.