Dec 23 (Reuters) - Talen Energy plans to contest the Federal Energy Regulatory Commission's (FERC) rejection of an amended interconnection agreement for an Amazon data center at its Pennsylvania nuclear plant, the company said on Monday.

The U.S. utility earlier this year sold a data center connected to its Susquehanna nuclear power plant to Amazon

and hoped to increase its capacity from 300 megawatts to 480 megawatts.

The deal, however, faced opposition from American Electric Power and Exelon .

FERC, in an order issued on Nov. 1, sided with the two regulated utilities and blocked the interconnection agreement.

Talen, last month, filed a request for a rehearing, to which the regulator responded on Monday, stating it would address the request in a future order.

As FERC did not decide on the rehearing request within 30 days, the decision to reject the amended interconnection agreement is now eligible for an appeal to a U.S. Circuit Court of Appeals, Talen Energy said in a statement.

Shares of the company, which have more than tripled this year, were up 0.6% in afternoon trading.

(Reporting by Vallari Srivastava in Bengaluru; Editing by Mohammed Safi Shamsi)

((Srivastava.Vallari@thomsonreuters.com;))