Economic activity in the U.S. manufacturing sector expanded at a slower pace in May than in April, according to the purchasing managers index for manufacturing released today by the Institute for Supply Management.

The institute’s manufacturing index fell to a reading of 53.5 in May from 54.8 in April. Readings above 50 indicate expansion. The average reading for the past 12 months was 53.1, with a high of 55.8 in June 2011.

The employment portion of the index expanded at a slower pace as well, slipping to a reading of 56.9 in May from 57.3 in April.