Serena Williams is vehemently speaking out against the anti-doping testing system in tennis. The seven-time Wimbledon champion expressed her disappointment with the system during a news conference on Sunday, ESPN reported.

What did Serena Williams say about tennis’ anti-doping system?

Williams, who is preparing to make her return to Wimbledon on Tuesday, said the protocol requires her to be available at busy times of the day and makes it possible for her to miss tests.

“They changed the rules now. I didn’t know some of the rules. So apparently if you miss a test outside of your window, it still counts as missed,” Williams said, per ESPN. “I’m like, I guess I can’t go pick up my kids. It’s unprofessional. I hate it. I think it’s necessary, but I think a lot of the stuff, if I want to go places outside of my window, I should be able to go without having it count as a missed test.”

What are the anti-doping rules?

The International Tennis Integrity Agency conducts a testing pool that includes the top 100 singles, doubles and wheelchair players, as well as returning players, according to the BBC. Athletes can face sanctions if they miss three out-of-competition tests within a 12-month period. The agency also requires players to provide their locations for one hour every day.

Williams said she almost didn’t return to tennis because she didn’t want to deal with the testing system.

“That was a big reason why I didn’t want to come back either, because it’s just so hard,” she said, per the BBC. “My life is busy, I run a [venture capital] company, I travel the world. I have children. It’s like I could be in so many different cities so many different times.”

The anti-doping system once again returned to the headlines last week when 2023 Wimbledon champion Marketa Vondrousova faced a four-year suspension for refusing a test. The ITIA describes its no-notice testing as a “fundamental pillar of an effective anti-doping program.”