Major League Baseball Players Association chief Tony Clark said Tuesday that the union has begun discussions with Major League Baseball about the composition of baseballs being used this season.

The makeup of baseballs used in the major leagues has become a hot-button topic with the increase in home runs hit in 2017.

There have been 3,343 home runs so far this season, the most at the All-Star break in MLB history, according to ESPN Stats & Information. The previous record was 3,312 in 2000.

MLB is on pace for 6,126 home runs this season, which would smash the single-season record, according to ESPN Stats & Information. The record is 5,693, set in 2000.

Clark, however, said the union is concerned about the baseballs with “health and safety” in mind.

“I will tell you that, in our dialogue with Major League Baseball, our concern is health and safety as well,” Clark said in a news conference with members of the Baseball Writers’ Association of America on Tuesday. “It’s not just what balls are going where and how hard they’re being thrown. There’s a health and safety issue there, too.”

Clark said there has been “a lot of rhetoric” regarding the baseballs being used this season. He said the union is “asking some questions ourselves, trying to appreciate what may be factual and what may be not.”

MLB commissioner Rob Manfred told the BBWAA writers Tuesday the league’s testing of the balls hasn’t revealed any difference from past years.

“I do know that we have done more testing of the baseball in the last couple of years than ever has been done historically, and we know with absolute certainty that the baseball falls within the specifications that have existed for many years,” Manfred said.

Manfred said there are “a number of factors in play here” from the way the game is being conducted at the major league level.

“Those changes are driven by the decisions of the 30 general managers and field managers who are trying to win a couple more games. There is a dramatically increased tolerance for strikeouts by offensive players, and there’s much more emphasis on the home run as the principal offensive tool in the game,” he said.

Manfred suggested there might be a difference with the bats players are using. He said that in the past, MLB has “kind of taken it for granted that bats aren’t different,” but now plans to spend more time looking at bats to determine the role they might play in the game’s dramatically increasing home run totals.

ESPN’s Jerry Crasnick contributed to this report.