It came as the bakery chain lifted its profit outlook for the year after surpassing pre-pandemic sales.
The company, which has more than 2,100 shops, said it has "not been immune”" to well-publicised supply chain pressures affecting the UK’s food and drinks firms.
It told shareholders on Tuesday morning that it has "seen some disruption to the availability of labour and supply of ingredients and products in recent months".
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Greggs also cautioned that it expects costs to climb at the end of 2021 and into next year.
"Food input inflation pressures are also increasing - whilst we have short-term protection as a result of our forward buying positions we expect costs to increase towards the end of 2021 and into 2022," the retail group said.
"Operational cost control has been good and the strong sales performance in the third quarter gives us confidence as we move into the autumn.”
The chain revealed that like-for-like sales increased by 3.5% in the third quarter of the year, against the same period from 2019.
It said its full-year performance is therefore expected to surpass the company’s previous expectations.
Greggs has increased its store estate by 68 stores since the start of the year and said it expects to have expanded by around 100 shops in 2021.
The steak bake maker said it will accelerate its opening programme next year, with around 150 net openings planned as it pushes towards its long-term goal of 3,000 stores across the country.
It said it also has ambitious plans to double its turnover to around £2.4 billion in the next five years, as it seeks to grow its delivery and evening operations further.
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