Institutional Shareholder Services Inc. (ISS), a proxy adviser firm, is advising MetroPCS shareholders to vote against the proposed merger deal between T-Mobile and MetroPCS.

ISS cited the negative market response the merger—which has resulted in a 14.4 percent price decline for PCS since the deal was announced—as well as an unjustifiably low equity split and PCS’s potential to thrive without merging.

ISS said in its report, "Absent merging with T-Mobile, PCS will have enough cash on its balance sheet to dedicate to new spectrum and could continue operating as a stand-alone company. It may well, as many commentators have suggested, have additional M&A opportunities in the offing, given its attractive assets."

MetroPCS last week sent a letter to shareholders insisting Deutsche Telekom was the only company offering to buy.

In a press release, MetroPCS responded, "Although we are pleased that ISS recognizes the thoroughness of the process undertaken by the MetroPCS board of directors, we strongly believe that ISS' report contains material flaws and reaches the wrong conclusion." MetroPCS went onto reiterate the points it made its shareholder letter.

P. Schoenfeld Asset Management LP, a firm that owns approximately 2.5 percent of MetroPCS, has actively protested the potential merger.

T-Mobile has cleared all necessary regulatory approvals for the merger. MetroPCS shareholders are expected to vote on the deal during a special meeting scheduled for April 12.