Analysts at Barclays have said a de-rating of UK pub stocks is "very likely" after MPs voted to scrap the 'beer tie', meaning that tenants are now allowed an independent rent review and will be able to buy beer on the open market.The government was defeated in a Commons vote on Tuesday with MPs voting 284 to 259 in favour of changing the Small Business, Enterprise and Employment Bill.The outcome means that large pub companies (pubcos) may be required to offer a market rent only (MRO) option - a 'free-of-tie' offer - to tenants."If this passes through the House of Lords and becomes law, this could have a material impact on the tenanted pub companies, Enterprise Inns and Punch Taverns," Barclays said.Analysts reassured investors that it may take some time for the results of the change to be seen - given that it is unlikely to pass into law immediately and rent reviews are every five years."It could be 2020 before all pubs have been converted to free of tie, which gives the pubcos breathing space from a disposal, conversion to managed/franchise, or capex perspective," the bank said.However, the eventual outcome will create "significant uncertainty" for the sector.Elsewhere, Barclays said that Marston's, Spirit and Greene King are relatively unaffected by the change, while cash-and-carry group Booker may be a beneficiary of tenants buying more supplies from wholesalers.Enterprise Inns was down 15.6% on Wednesday morning, while Punch Taverns dropped 10.9%.