The number of people screened by CervicalCheck decreased by over a third last year.
The service stopped last March due to the first lockdown and did not resume until July.
It is now operational and people are being encouraged to make their cervical screening appointments as usual.
But Dr Nóirín Russell, the clinical director of CervicalCheck, says 70,000 fewer people were screened last year.
"We screened approximately 139,000 women in primary care last year," Dr Russell said.
"We know when we look back on 2019 that we screened 210,000 women.
"We would estimate that around 70,000 to maybe 100,000 women who were due their screening test in 2020 need to be looked after in 2021."
CervicalCheck campaigner Vicky Phelan says she has 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.
"If you have symptoms, you need to go see your GP because if you have symptoms of cervical cancer - that could be bleeding between periods, bleeding after sex, any of those type of symptoms - you really need to see your GP and get to see a gynecologist as urgently as possible."
Ms Phelan is currently in the US for a treatment that she hopes will prolong her life.
She is taking part in a trial and has said that after two months they should know if the treatment is working.
She headed over to the States on January 10.