Proxy advisor Glass Lewis has advised shareholders at MetroPCS to veto the proposed merger of with T-Mobile USA, pressuring Deutsche Telekom AG to give better deal.

In a released reported, Glass Lewis highlighted its belief that the contribution of MetroPCS to the combined firm will be undervalued by the proposed merger. The advisor added that shareholders at MetroPCS could get additional value in the short term even without the merger with Deutche Telekom AG's U.S. business unit.

Glass Lewis' advisory came after larger proxy firm ISS urged MetroPCS shareholders to vote against the T-Mobile USA due to negative market response to the merger. ISS said in a released statement that MetroPCS has the potential to stand as a single company.

Major MetroPCS shareholders P. Schoenfeld Asset Management and Paulson & Co. had already made commitment that they would block the deal on concerns over lower valuations and debts that the combined firm will likely incur.