Hauliers met AMs at a motorway service station to hand in a petition
Conservatives have written to south Wales' chief constable over the way a hauliers' fuel protest was handled.
More than 150 lorries travelled from west Wales on Tuesday, but the Tories are questioning why they did not hand over a petition in Cardiff Bay.
However, police said the hauliers rejected an offer for a limited number of lorries to drive to the home of the Welsh assembly, the Senedd.
Instead, the petition was handed to Tory AMs on the outskirts of the city.
Welsh Tory leader Nick Bourne said that raised concerns.
"The situation that arose on Tuesday raises questions about the democratic rights of people in Wales and their legitimate expectation to be able to present petitions at the National Assembly," he said.
"If the electorate feels so strongly about an issue that they want to present a written document to AMs, then it is important we give them the chance to do that."
However, South Wales Police strongly defended their actions.
Assistant chief constable Dave Morris said that "at no time did South Wales Police aim to prevent the protestors from submitting their petition to the Senedd".
"However, whilst we were prepared to facilitate the protest, we have a responsibility to ensure that disruption to the general public and other road users is kept to an absolute minimum.
"For that reason, it was agreed three days before the protest that five lorries would be permitted to travel to the Senedd to make the presentation."
But Nr Morris said the hauliers then requested that the convoy met at the M4 motorway services, which he said his officers facilitated.
However, Mr Bourne said following the protest he had now contacted assembly Presiding Officer Lord Elis Thomas to request details of guidelines surrounding access to the assembly for protesters and petitioners.