NEW YORK (Reuters) - U.S. services sector expansion eased for a third straight month in June, pressured by a slowdown in employment and output growth, an industry report showed on Monday.

Financial firm Markit said its final reading of its Purchasing Managers Index for the services sector slipped to 54.8 in June, matching the preliminary reading.

A reading over 50 signals expansion in economic activity.

Markit's May reading of new business at service companies ticked higher from the prior month and was above the preliminary reading.

The services index's employment component declined to 54.1 from the 55.5 in May, which was the highest level since June 2014.

Markit's composite PMI, a weighted average of its manufacturing and services indexes, was 54.6, also matching the preliminary reading for June and down from the 56.0 in May. Last week, Markit's final read on U.S. manufacturing activity showed growth fell to its slowest pace since October 2013 in June.

"Although still signaling moderate growth in June, the manufacturing and service sector surveys indicate that the rate of economic expansion has slowed markedly since the start of the quarter, when business was boosted by a rebound from weather related weakness," Markit Chief Economist Chris Williamson said in a statement.

"The loss of growth momentum seen in the surveys means GDP growth could slacken off again in the third quarter and hiring could likewise ease off."

(Reporting by Chuck Mikolajczak, Editing by Chizu Nomiyama)