Flat glass prices spiked 2.8 percent in June, after dipping 1.1 percent in April and leveling out with a 0.1-percent increase in May, according to the latest Producer Price Index Report (PPI) issued by the U.S. Labor Department.

The PPI program measures the average change over time in the selling prices received by domestic producers for their output, according to the U.S. Bureau of Labor Statistics (BLS). The prices included in the PPI are from the first commercial transaction for many products and some services.

The flat glass index sits at 125.5, and prices are up 4.0 percent from June 2014.

In another report, import prices for glass and glassware increased 0.2 in June, following an identical rise in both April and May. Prices in that category are up 0.2 percent from June 2014, with an index of 129.9.

Export prices for glass and glassware, meanwhile, went unchanged in June after dropping 0.3 percent in both April and May. Those prices are up 0.3 percent from this time last year and have an index of 99.0.

Prices of construction materials fell 0.2 percent in June after dipping 0.3 percent in May. They saw an increase of 0.4 percent in April after dropping by that same rate in March. Prices in that category are up 0.2 percent from June 2014. Final demand for construction rose by 0.1 percent for the fifth straight month. Those prices are up 1.8 percent from a year ago.

On the whole, the PPI for final demand jumped 0.4 percent in June, seasonally adjusted, following an increase of 0.5 in May. On an unadjusted basis, the index for final demand is down 0.7 percent for the 12 months ended in June, marking the fifth straight 12-month decrease.

Overall prices for U.S. imports saw a slight 0.1-percent decrease in June after increasing 1.2 percent the previous month. Export prices dropped 0.2 percent in June after rising 0.6 percent in May.