(Reuters) - UBS Investment Research downgraded ATMI Inc to "sell" from "neutral" citing macroeconomic uncertainty and lower orders from its biggest customer.

The brokerage said ATMI's results in the second half of the year could be hit by a fall in orders from Taiwan Semiconductor Manufacturing Co Ltd (TSMC) <2330.TW>, the world's biggest contract chipmaker, in the current quarter.

TSMC and other chipmakers have warned of a slowdown in sales as they face a downturn in global technology spending as Europe's woes continue to dent demand and China's economy slows.

TSMC is ATMI's largest customer and accounts for about 13 percent of its sales, UBS analyst Stephen Chin said in a note.

TSMC Chairman Morris Chang said at an investor conference last week that inventory levels at its clients have been increasing due to a deteriorating macroeconomic environment.

Analyst Chin cut his price target on Danbury, Connecticut-based ATMI's stock to $16 from $22.

Shares of ATMI fell were down 6 percent at $19.13 on Monday afternoon on the Nasdaq.

(Reporting by Shubham Singhal in Bangalore; Editing by Roshni Menon)