Clearwire investor Crest Financial stepped up its efforts to block the sale of the US wholesale operator to majority shareholder Sprint by requesting the Federal Communications Commission (FCC) blocks the deal, reports Reuters.

Dave Schumacher, general counsel of Crest, said in a press call that Sprint’s offer of $2.97 per share for around 50 percent of Clearwire “grossly undervalues” the company. Reports suggest the bid was the maximum permitted by Sprint’s prospective merger partner Softbank.

According to Schumacher, the investment fund will argue to the FCC that the deal artificially undervalues Clearwire’s spectrum holdings. This will have the knock-on effect of devaluing future revenue for the US government when it auctions off spectrum licenses, meaning the deal is bad for Clearwire shareholders and the “public at large”.

Crest — which recently upped its stake in Clearwire from 6.62 percent to 8.34 percent — has already filed a class action on behalf of itself and other Clearwire investors in the Court of Chancery in Delaware in an attempt to permanently block the deal.

Clearwire chief executive Erik Prusch has said the company does not have many attractive alternatives to the Sprint deal, as it requires funding to upgrade its network and risks bankruptcy if a solution isn’t found.

Sprint has said it had the support of three large Clearwire investors, Comcast, Intel and Bright House Networks, which collectively hold 13 percent of the company’s stock. However, Schumacher said Crest will attempt to prevent the three companies voting due to their affiliation with Sprint.

Schumacher indicated that Crest also plans to protest the proposed $20 billion deal for Japanese operator group Softbank to acquire 70 percent of Sprint.

A Kansas court last week declined Sprint’s request for an early dismissal of a lawsuit filed by a union pension fund holding Sprint stock.  The suit alleges that Sprint CEO Dan Hesse rushed merger talks with Softbank meaning he did not get a fair price for the stake the Japanese group is planning to acquire.