Senator Mac Harb has repaid more than $51,000 in expenses, but the senator has done so under protest as he continues his legal challenge, arguing that the Senate denied him his basic legal rights and procedural fairness.

The Senate issued a news release Friday confirming it had received a cheque from Harb to the Receiver General for Canada in the amount of $51,482.90.

The release said Harb had advised the Senate that the cheque was submitted "under protest, which means that [Harb] vigorously denies any liability and he intends to pursue his Judicial Review Application in the Ontario Divisional Court."

Harb, who left the Liberal caucus to sit as an Independent amid the spending controversy, faced scrutiny over expenses related to the house he called his primary residence near Pembroke, Ont.

In May, the Senate internal economy committee said Harb owed $51,000 in expenses claimed over the past two years. In June, Harb was sent a letter ordering him to pay that amount.

In a letter from the chair of the internal economy committee, the Senate advised Harb to repay more than $231,000 claimed since 2005 or face an extensive audit of his expense claims over that period.

Senators whose primary residence is at least 100 kilometres from Ottawa are permitted to charge living and travel expenses.

Harb is not the only senator facing scrutiny over expenses. Mike Duffy, Pamela Wallin and Patrick Brazeau have also had their expenses examined.

Brazeau, who was facing a June 30 deadline to repay $48,000, was sent a letter advising him that 20 per cent of his pay will be docked until the housing and travel expenses are repaid.

Brazeau's office said earlier this week that he had not yet received notice from the Senate about the wage reduction.

Mike Duffy's expense issues have been sent to the RCMP for review, and recent court documents suggest that the force is also gathering documents about Harb's claims.

Duffy, who faced questions about his residency status in P.E.I., released a statement in April saying he had repaid more than $90,000 in housing and living expenses. It was later revealed that the prime minister's chief of staff, Nigel Wright, had written a personal cheque to cover Duffy's expenses.

Senator Pamela Wallin's expenses were being reviewed in an independent audit, the results of which are not yet available. Wallin has already repaid more than $40,000 in expense claims, but it's alleged the former journalist could face a request to repay even more.