Stamp duty rates should be halved, with a view to abolishing the tax entirely, according to the TaxPayers' Alliance.
The group argued that a recent three percentage point increase to stamp duty rates will end up driving up rents, as the costs are passed on to tenants.
The increase, which came into force on April 1, applies to people buying second homes, including buy-to-let investors.
The TaxPayers' Alliance described stamp duty as a "badly-designed tax which gums up property markets".
It said the three percentage point increase should be done away with and all stamp duty rates should be halved immediately, with a view to abolishing the tax entirely.
The campaign group said the stamp duty hike for landlords, along with other measures, will tighten housing supply in the lettings market, raising rents.
It said stamp duty is an "unfair tax which stops people from buying their own home, settling down with a family, moving for work or downsizing".
The group argued that planning restrictions should also be reformed to declassify some green belt land and allow taller, denser construction in urban areas.
Jonathan Isaby, chief executive of the TaxPayers' Alliance, said: "For decades politicians have failed to tackle the root causes of the housing crisis: a chronic lack of supply. What's more, stamp duty is still punitively high and gimmicky tweaks to the tax system will ultimately end up penalising tenants and increasing rents.
"The new Chancellor should now seize the opportunity to drastically simplify and reduce property taxes, while removing planning restrictions which prevent huge swathes of land from being built on for no good reason at all."