Major League Baseball informed clubs and players Thursday afternoon that its efforts to crack down on pitchers' use of illegal substances will be enhanced this season, according to sources informed of the contents of a league memo.

The enhanced examinations will entail more detailed inspections by umpires and inspections that occur more often than they have over the past 21 months.

"Umpires have been instructed to increase the frequency and scope of foreign substance checks this year, including randomized checks of fingers (including removal of rings worn on either hand of pitchers), hands, hats, gloves, belts/waistlines, and pants," the memo states. "Pitchers may be subject to checks before or after innings in which they pitch, and managers may make inspection requests of a pitcher or position player either before or after an at-bat."

According to the memo, umpires can focus on "suspicious behavior by players that suggests the potential use of foreign substances."