The number of women screened by CervicalCheck decreased by over a third last year.
The service stopped last March due to the first lockdown and didn't resume until July.
It's now operational and women are being encouraged to make their cervical screening appointments as usual.
But Dr Nóirín Russell, the clinical director of CervicalCheck, says 70,000 fewer women were screened last year.
"We screened approximately 139,000 women in primary care last year. We know when we look back at 2019 that we screened 210,000 women.
"We would estimate that there is about 70,000, maybe 100,000 women, who were due their screening test in 2020, who need to be looked after in 2021."
CervicalCheck campaigner Vicky Phelan says she's been contacted by many concerned women who haven't been able to get smear tests.
She is urging anyone with symptoms of cervical cancer to contact their GP immediately.
"A lot of women would have contacted me worried about it, saying that they couldn't get their smears.
"What I would say to anybody that if you have symptoms, a smear is not the way to go. And I know that the new head of CervicalCheck would say the same thing.
"If you have symptoms, you need to go see your GP. Because if you symptoms of Cervical cancer, that could be bleeding in between periods, bleeding after sex, you really need to go see a GP and see a gynecologist as urgently as possible."